Approximately how long do bacteria live for?

Approximately how long do bacteria live for?

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I would like to know how many days or years do the bacteria live approximately.

They're effectively immortal, albeit in a Phoenix-rising-from-the-ashes sort of way.

In general, a bacterial cell will divide as soon as it's biochemically able to do so, leaving behind two daughter cells. Neither daughter cell is actually the same as the mother cell, so in one sense the mother cell will have "died". On the other hand, the daughter cells are genetically identical to the mother cell and all of the physical material present in each of the daughter cells at the moment right after they split came from the mother cell.

What Is the Life Cycle of Bacteria?

The life cycle of bacteria consists of four main phases: the lag phase, the exponential or log phase, the stationary phase and the death phase. Factors that trigger bacteria growth heavily rely on this life cycle. Bacteria multiply through a process known as binary fission.

During the lag phase, bacteria do not grow. They only adjust to their environment and metabolize, producing the amino acids and vitamins that they need for division. In this stage, they also make copies of DNA. If there are enough nutrients available, this phase may be very short.

In the exponential or log phase, bacteria multiply rapidly. Under favorable conditions, bacteria can double in approximately 15 minutes. However, bacteria sometimes takes days to multiply. The amount of time a culture takes to double is referred to as "generation time".

Bacteria multiply through a process known as binary fission. For a bacterium to multiply, its DNA copy drifts to two opposite sides of the membrane, creating identical daughter cells which multiply again.

The stationary stage is characterized by a decline in bacteria growth. The decline results from growth-inhibiting factors, such as the formation of inhibitory products or depletion of essential nutrients. In this phase, growth and death rates are equal. In the death phase, bacteria lose the ability to reproduce.


Probiotics are living micro-organisms which exert a positive health benefit when you eat them. According to "The American Journal of Clinical Nutrition," some of the most common probiotics belong to the species Lactobacillus, Bifidobacterium and Saccharomyces. Probiotics have been used anciently the name "pro" means "for" in Latin and "biotic" means "life." Antibiotics are made up of the two Latin names: "anti" meaning "against" and "biotic" for "life." Probiotics are "for life" and antibiotics are "against life." Antibiotics have saved lives and have a valuable place in maintaining health. Probiotics ensure that good bacteria keeps your gut healthy. Once in the intestines, probiotics create an environment where good bacteria thrives and bad bacteria is less likely to stay alive.

Bacteria: Fossil Record

It may seem surprising that bacteria can leave fossils at all. However, one particular group of bacteria, the cyanobacteria or "blue-green algae," have left a fossil record that extends far back into the Precambrian - the oldest cyanobacteria-like fossils known are nearly 3.5 billion years old, among the oldest fossils currently known. Cyanobacteria are larger than most bacteria, and may secrete a thick cell wall. More importantly, cyanobacteria may form large layered structures, called stromatolites (if more or less dome-shaped) or oncolites (if round). These structures form as a mat of cyanobacteria grows in an aquatic environment, trapping sediment and sometimes secreting calcium carbonate. When sectioned very thinly, fossil stromatolites may be found to contain exquisitely preserved fossil cyanobacteria and algae.

The picture above is a short chain of cyanobacterial cells, from the Bitter Springs Chert of northern Australia (about 1 billion years old). Very similar cyanobacteria are alive today in fact, most fossil cyanobacteria can almost be referred to living genera. Compare this fossil cyanobacterium with this picture of the living cyanobacterium Oscillatoria:

The group shows what is probably the most extreme conservatism of morphology of any organisms.

Aside from cyanobacteria, identifiable fossil bacteria are not particularly widespread. However, under certain chemical conditions, bacterial cells can be replaced with minerals, notably pyrite or siderite (iron carbonate), forming replicas of the once-living cells, or pseudomorphs. Some bacteria secrete iron-coated sheaths that sometimes fossilize. Others may bore into shells or rocks and form microscopic canals within the shell such bacteria are referred to as endolithic, and their borings can be recognized all through the Phanerozoic. Bacteria have also been found in amber -- fossilized tree resin -- and in mummified tissues. It is also sometimes possible to infer the presence of disease-causing bacteria from fossil bones that show signs of having been infected when the animal was alive. Perhaps most amazing are the fossils left by magnetobacteria -- a group of bacteria which form tiny, nanometer-sized crystals of magnetite (iron oxide) inside their cells. Magnetite crystals identifiable as bacterial products have been found in rocks as old as two billion years -- at a size of a few hundred millionths of a meter, these hold the record for the smallest fossils.

NEWS FLASH!One of the hottest science news stories of the decade is the discovery of possible remains of bacteria-like organisms on a meteorite from Mars. But are they really fossils? How would we be able to find out whether or not they are real? And what could they tell us about the history of Mars -- and of life on our own planet? Paleontologists are working together with space scientists to try and answer some basic questions about the possible "Martian bacteria." There will eventually be an exhibit on this server dealing with the "Martian microbes." Until it's ready, you can view photographs and news articles about the find, or learn more about Mars meteorites courtesy of the NASA Jet Propulsion Laboratory. --> Read a UCMP Research Report: "Bacteria and protozoa from middle Cretaceous amber of Ellsworth County, Kansas." Find out more about fossilized filamentous bacteria and other microbes, found in Cretaceous amber -- a unique mode of preservation. This report was originally published in PaleoBios 17(1): 20-26. Dr. Raul Cano, at California Polytechnic State University at San Luis Obispo, has succeeded in isolating and reviving bacteria taken from inside fossilized insects trapped in amber. Read all about it!

Bitter Springs chert fossil image provided by J. William Schopf. The image of Oscillatoria was provided by Alejandro Lopez-Cortes (CIBNOR, Mexico), Mark Schneegurt (Wichita State University), and Cyanosite.


The oldest meteorite fragments found on Earth are about 4.54 billion years old this, coupled primarily with the dating of ancient lead deposits, has put the estimated age of Earth at around that time. [40] The Moon has the same composition as Earth's crust but does not contain an iron-rich core like the Earth's. Many scientists think that about 40 million years after the formation of Earth, it collided with a body the size of Mars, throwing into orbit crust material that formed the Moon. Another hypothesis is that the Earth and Moon started to coalesce at the same time but the Earth, having much stronger gravity than the early Moon, attracted almost all the iron particles in the area. [41]

Until 2001, the oldest rocks found on Earth were about 3.8 billion years old, [42] [40] leading scientists to estimate that the Earth's surface had been molten until then. Accordingly, they named this part of Earth's history the Hadean. [43] However, analysis of zircons formed 4.4 Ga indicates that Earth's crust solidified about 100 million years after the planet's formation and that the planet quickly acquired oceans and an atmosphere, which may have been capable of supporting life. [44] [45] [46]

Evidence from the Moon indicates that from 4 to 3.8 Ga it suffered a Late Heavy Bombardment by debris that was left over from the formation of the Solar System, and the Earth should have experienced an even heavier bombardment due to its stronger gravity. [43] [47] While there is no direct evidence of conditions on Earth 4 to 3.8 Ga, there is no reason to think that the Earth was not also affected by this late heavy bombardment. [48] This event may well have stripped away any previous atmosphere and oceans in this case gases and water from comet impacts may have contributed to their replacement, although outgassing from volcanoes on Earth would have supplied at least half. [49] However, if subsurface microbial life had evolved by this point, it would have survived the bombardment. [50]

The earliest identified organisms were minute and relatively featureless, and their fossils look like small rods that are very difficult to tell apart from structures that arise through abiotic physical processes. The oldest undisputed evidence of life on Earth, interpreted as fossilized bacteria, dates to 3 Ga. [51] Other finds in rocks dated to about 3.5 Ga have been interpreted as bacteria, [52] with geochemical evidence also seeming to show the presence of life 3.8 Ga. [53] However, these analyses were closely scrutinized, and non-biological processes were found which could produce all of the "signatures of life" that had been reported. [54] [55] While this does not prove that the structures found had a non-biological origin, they cannot be taken as clear evidence for the presence of life. Geochemical signatures from rocks deposited 3.4 Ga have been interpreted as evidence for life, [51] [56] although these statements have not been thoroughly examined by critics.

Evidence for fossilized microorganisms considered to be 3.77 billion to 4.28 billion years old was found in the Nuvvuagittuq Greenstone Belt in Quebec, Canada, [16] although the evidence is disputed as inconclusive. [57]

Biologists reason that all living organisms on Earth must share a single last universal ancestor, because it would be virtually impossible that two or more separate lineages could have independently developed the many complex biochemical mechanisms common to all living organisms. [59] [60]

Independent emergence on Earth Edit

Life on Earth is based on carbon and water. Carbon provides stable frameworks for complex chemicals and can be easily extracted from the environment, especially from carbon dioxide. [46] There is no other chemical element whose properties are similar enough to carbon's to be called an analogue silicon, the element directly below carbon on the periodic table, does not form very many complex stable molecules, and because most of its compounds are water-insoluble and because silicon dioxide is a hard and abrasive solid in contrast to carbon dioxide at temperatures associated with living things, it would be more difficult for organisms to extract. The elements boron and phosphorus have more complex chemistries, but suffer from other limitations relative to carbon. Water is an excellent solvent and has two other useful properties: the fact that ice floats enables aquatic organisms to survive beneath it in winter and its molecules have electrically negative and positive ends, which enables it to form a wider range of compounds than other solvents can. Other good solvents, such as ammonia, are liquid only at such low temperatures that chemical reactions may be too slow to sustain life, and lack water's other advantages. [61] Organisms based on alternative biochemistry may, however, be possible on other planets. [62]

Research on how life might have emerged from non-living chemicals focuses on three possible starting points: self-replication, an organism's ability to produce offspring that are very similar to itself metabolism, its ability to feed and repair itself and external cell membranes, which allow food to enter and waste products to leave, but exclude unwanted substances. [63] Research on abiogenesis still has a long way to go, since theoretical and empirical approaches are only beginning to make contact with each other. [64] [65]

Replication first: RNA world Edit

Even the simplest members of the three modern domains of life use DNA to record their "recipes" and a complex array of RNA and protein molecules to "read" these instructions and use them for growth, maintenance and self-replication. The discovery that some RNA molecules can catalyze both their own replication and the construction of proteins led to the hypothesis of earlier life-forms based entirely on RNA. [66] These ribozymes could have formed an RNA world in which there were individuals but no species, as mutations and horizontal gene transfers would have meant that the offspring in each generation were quite likely to have different genomes from those that their parents started with. [67] RNA would later have been replaced by DNA, which is more stable and therefore can build longer genomes, expanding the range of capabilities a single organism can have. [67] [68] [69] Ribozymes remain as the main components of ribosomes, modern cells' "protein factories." [70] Evidence suggests the first RNA molecules formed on Earth prior to 4.17 Ga. [71]

Although short self-replicating RNA molecules have been artificially produced in laboratories, [72] doubts have been raised about whether natural non-biological synthesis of RNA is possible. [73] The earliest "ribozymes" may have been formed of simpler nucleic acids such as PNA, TNA or GNA, which would have been replaced later by RNA. [74] [75]

In 2003, it was proposed that porous metal sulfide precipitates would assist RNA synthesis at about 100 °C (212 °F) and ocean-bottom pressures near hydrothermal vents. Under this hypothesis, lipid membranes would be the last major cell components to appear and, until then, the protocells would be confined to the pores. [76]

Metabolism first: Iron–sulfur world Edit

A series of experiments starting in 1997 showed that early stages in the formation of proteins from inorganic materials including carbon monoxide and hydrogen sulfide could be achieved by using iron sulfide and nickel sulfide as catalysts. Most of the steps required temperatures of about 100 °C (212 °F) and moderate pressures, although one stage required 250 °C (482 °F) and a pressure equivalent to that found under 7 kilometres (4.3 mi) of rock. Hence it was suggested that self-sustaining synthesis of proteins could have occurred near hydrothermal vents. [77]

Membranes first: Lipid world Edit

It has been suggested that double-walled "bubbles" of lipids like those that form the external membranes of cells may have been an essential first step. [78] Experiments that simulated the conditions of the early Earth have reported the formation of lipids, and these can spontaneously form liposomes, double-walled "bubbles," and then reproduce themselves. [46] Although they are not intrinsically information-carriers as nucleic acids are, they would be subject to natural selection for longevity and reproduction. Nucleic acids such as RNA might then have formed more easily within the liposomes than they would have outside. [79]

The clay hypothesis Edit

RNA is complex and there are doubts about whether it can be produced non-biologically in the wild. [73] Some clays, notably montmorillonite, have properties that make them plausible accelerators for the emergence of an RNA world: they grow by self-replication of their crystalline pattern they are subject to an analog of natural selection, as the clay "species" that grows fastest in a particular environment rapidly becomes dominant and they can catalyze the formation of RNA molecules. [80] Although this idea has not become the scientific consensus, it still has active supporters. [81]

Research in 2003 reported that montmorillonite could also accelerate the conversion of fatty acids into "bubbles," and that the "bubbles" could encapsulate RNA attached to the clay. These "bubbles" can then grow by absorbing additional lipids and then divide. The formation of the earliest cells may have been aided by similar processes. [82]

A similar hypothesis presents self-replicating iron-rich clays as the progenitors of nucleotides, lipids and amino acids. [83]

Life "seeded" from elsewhere Edit

The Panspermia hypothesis does not explain how life arose in the first place, but simply examines the possibility of it coming from somewhere other than the Earth. The idea that life on Earth was "seeded" from elsewhere in the Universe dates back at least to the Greek philosopher Anaximander in the sixth century BCE. [84] In the twentieth century it was proposed by the physical chemist Svante Arrhenius, [85] by the astronomers Fred Hoyle and Chandra Wickramasinghe, [86] and by molecular biologist Francis Crick and chemist Leslie Orgel. [87]

There are three main versions of the "seeded from elsewhere" hypothesis: from elsewhere in our Solar System via fragments knocked into space by a large meteor impact, in which case the most credible sources are Mars [88] and Venus [89] by alien visitors, possibly as a result of accidental contamination by microorganisms that they brought with them [87] and from outside the Solar System but by natural means. [85] [88]

Experiments in low Earth orbit, such as EXOSTACK, demonstrated that some microorganism spores can survive the shock of being catapulted into space and some can survive exposure to outer space radiation for at least 5.7 years. [90] [91] Scientists are divided over the likelihood of life arising independently on Mars, [92] or on other planets in our galaxy. [88]

Microbial mats are multi-layered, multi-species colonies of bacteria and other organisms that are generally only a few millimeters thick, but still contain a wide range of chemical environments, each of which favors a different set of microorganisms. [93] To some extent each mat forms its own food chain, as the by-products of each group of microorganisms generally serve as "food" for adjacent groups. [94]

Stromatolites are stubby pillars built as microorganisms in mats slowly migrate upwards to avoid being smothered by sediment deposited on them by water. [93] There has been vigorous debate about the validity of alleged fossils from before 3 Ga, [95] with critics arguing that so-called stromatolites could have been formed by non-biological processes. [54] In 2006, another find of stromatolites was reported from the same part of Australia as previous ones, in rocks dated to 3.5 Ga. [96]

In modern underwater mats the top layer often consists of photosynthesizing cyanobacteria which create an oxygen-rich environment, while the bottom layer is oxygen-free and often dominated by hydrogen sulfide emitted by the organisms living there. [94] It is estimated that the appearance of oxygenic photosynthesis by bacteria in mats increased biological productivity by a factor of between 100 and 1,000. The reducing agent used by oxygenic photosynthesis is water, which is much more plentiful than the geologically produced reducing agents required by the earlier non-oxygenic photosynthesis. [97] From this point onwards life itself produced significantly more of the resources it needed than did geochemical processes. [98] Oxygen is toxic to organisms that are not adapted to it, but greatly increases the metabolic efficiency of oxygen-adapted organisms. [99] [100] Oxygen became a significant component of Earth's atmosphere about 2.4 Ga. [101] Although eukaryotes may have been present much earlier, [102] [103] the oxygenation of the atmosphere was a prerequisite for the evolution of the most complex eukaryotic cells, from which all multicellular organisms are built. [104] The boundary between oxygen-rich and oxygen-free layers in microbial mats would have moved upwards when photosynthesis shut down overnight, and then downwards as it resumed on the next day. This would have created selection pressure for organisms in this intermediate zone to acquire the ability to tolerate and then to use oxygen, possibly via endosymbiosis, where one organism lives inside another and both of them benefit from their association. [18]

Cyanobacteria have the most complete biochemical "toolkits" of all the mat-forming organisms. Hence they are the most self-sufficient of the mat organisms and were well-adapted to strike out on their own both as floating mats and as the first of the phytoplankton, providing the basis of most marine food chains. [18]

Chromatin, nucleus, endomembrane system, and mitochondria Edit

Eukaryotes may have been present long before the oxygenation of the atmosphere, [102] but most modern eukaryotes require oxygen, which their mitochondria use to fuel the production of ATP, the internal energy supply of all known cells. [104] In the 1970s it was proposed and, after much debate, widely accepted that eukaryotes emerged as a result of a sequence of endosymbiosis between prokaryotes. For example: a predatory microorganism invaded a large prokaryote, probably an archaean, but the attack was neutralized, and the attacker took up residence and evolved into the first of the mitochondria one of these chimeras later tried to swallow a photosynthesizing cyanobacterium, but the victim survived inside the attacker and the new combination became the ancestor of plants and so on. After each endosymbiosis began, the partners would have eliminated unproductive duplication of genetic functions by re-arranging their genomes, a process which sometimes involved transfer of genes between them. [107] [108] [109] Another hypothesis proposes that mitochondria were originally sulfur- or hydrogen-metabolising endosymbionts, and became oxygen-consumers later. [110] On the other hand, mitochondria might have been part of eukaryotes' original equipment. [111]

There is a debate about when eukaryotes first appeared: the presence of steranes in Australian shales may indicate that eukaryotes were present 2.7 Ga [103] however, an analysis in 2008 concluded that these chemicals infiltrated the rocks less than 2.2 Ga and prove nothing about the origins of eukaryotes. [112] Fossils of the algae Grypania have been reported in 1.85 billion-year-old rocks (originally dated to 2.1 Ga but later revised [21] ), and indicates that eukaryotes with organelles had already evolved. [113] A diverse collection of fossil algae were found in rocks dated between 1.5 and 1.4 Ga. [114] The earliest known fossils of fungi date from 1.43 Ga. [115]

Plastids Edit

Plastids, the superclass of organelles of which chloroplasts are the best-known exemplar, are thought to have originated from endosymbiotic cyanobacteria. The symbiosis evolved around 1.5 Ga and enabled eukaryotes to carry out oxygenic photosynthesis. [104] Three evolutionary lineages of photosynthetic plastids have since emerged in which the plastids are named differently: chloroplasts in green algae and plants, rhodoplasts in red algae and cyanelles in the glaucophytes. [116]

Evolution of sexual reproduction Edit

The defining characteristics of sexual reproduction in eukaryotes are meiosis and fertilization. There is much genetic recombination in this kind of reproduction, in which offspring receive 50% of their genes from each parent, [117] in contrast with asexual reproduction, in which there is no recombination. Bacteria also exchange DNA by bacterial conjugation, the benefits of which include resistance to antibiotics and other toxins, and the ability to utilize new metabolites. [118] However, conjugation is not a means of reproduction, and is not limited to members of the same species – there are cases where bacteria transfer DNA to plants and animals. [119]

On the other hand, bacterial transformation is clearly an adaptation for transfer of DNA between bacteria of the same species. Bacterial transformation is a complex process involving the products of numerous bacterial genes and can be regarded as a bacterial form of sex. [120] [121] This process occurs naturally in at least 67 prokaryotic species (in seven different phyla). [122] Sexual reproduction in eukaryotes may have evolved from bacterial transformation. [123]

The disadvantages of sexual reproduction are well-known: the genetic reshuffle of recombination may break up favorable combinations of genes and since males do not directly increase the number of offspring in the next generation, an asexual population can out-breed and displace in as little as 50 generations a sexual population that is equal in every other respect. [117] Nevertheless, the great majority of animals, plants, fungi and protists reproduce sexually. There is strong evidence that sexual reproduction arose early in the history of eukaryotes and that the genes controlling it have changed very little since then. [124] How sexual reproduction evolved and survived is an unsolved puzzle. [125]

The Red Queen hypothesis suggests that sexual reproduction provides protection against parasites, because it is easier for parasites to evolve means of overcoming the defenses of genetically identical clones than those of sexual species that present moving targets, and there is some experimental evidence for this. However, there is still doubt about whether it would explain the survival of sexual species if multiple similar clone species were present, as one of the clones may survive the attacks of parasites for long enough to out-breed the sexual species. [117] Furthermore, contrary to the expectations of the Red Queen hypothesis, Kathryn A. Hanley et al. found that the prevalence, abundance and mean intensity of mites was significantly higher in sexual geckos than in asexuals sharing the same habitat. [127] In addition, biologist Matthew Parker, after reviewing numerous genetic studies on plant disease resistance, failed to find a single example consistent with the concept that pathogens are the primary selective agent responsible for sexual reproduction in the host. [128]

Alexey Kondrashov's deterministic mutation hypothesis (DMH) assumes that each organism has more than one harmful mutation and the combined effects of these mutations are more harmful than the sum of the harm done by each individual mutation. If so, sexual recombination of genes will reduce the harm that bad mutations do to offspring and at the same time eliminate some bad mutations from the gene pool by isolating them in individuals that perish quickly because they have an above-average number of bad mutations. However, the evidence suggests that the DMH's assumptions are shaky because many species have on average less than one harmful mutation per individual and no species that has been investigated shows evidence of synergy between harmful mutations. [117]

The random nature of recombination causes the relative abundance of alternative traits to vary from one generation to another. This genetic drift is insufficient on its own to make sexual reproduction advantageous, but a combination of genetic drift and natural selection may be sufficient. When chance produces combinations of good traits, natural selection gives a large advantage to lineages in which these traits become genetically linked. On the other hand, the benefits of good traits are neutralized if they appear along with bad traits. Sexual recombination gives good traits the opportunities to become linked with other good traits, and mathematical models suggest this may be more than enough to offset the disadvantages of sexual reproduction. [125] Other combinations of hypotheses that are inadequate on their own are also being examined. [117]

The adaptive function of sex today remains a major unresolved issue in biology. The competing models to explain the adaptive function of sex were reviewed by John A. Birdsell and Christopher Wills. [129] The hypotheses discussed above all depend on the possible beneficial effects of random genetic variation produced by genetic recombination. An alternative view is that sex arose and is maintained, as a process for repairing DNA damage, and that the genetic variation produced is an occasionally beneficial byproduct. [123] [130]

Multicellularity Edit

The simplest definitions of "multicellular," for example "having multiple cells," could include colonial cyanobacteria like Nostoc. Even a technical definition such as "having the same genome but different types of cell" would still include some genera of the green algae Volvox, which have cells that specialize in reproduction. [131] Multicellularity evolved independently in organisms as diverse as sponges and other animals, fungi, plants, brown algae, cyanobacteria, slime molds and myxobacteria. [21] [132] For the sake of brevity, this article focuses on the organisms that show the greatest specialization of cells and variety of cell types, although this approach to the evolution of biological complexity could be regarded as "rather anthropocentric." [22]

The initial advantages of multicellularity may have included: more efficient sharing of nutrients that are digested outside the cell, [134] increased resistance to predators, many of which attacked by engulfing the ability to resist currents by attaching to a firm surface the ability to reach upwards to filter-feed or to obtain sunlight for photosynthesis [135] the ability to create an internal environment that gives protection against the external one [22] and even the opportunity for a group of cells to behave "intelligently" by sharing information. [133] These features would also have provided opportunities for other organisms to diversify, by creating more varied environments than flat microbial mats could. [135]

Multicellularity with differentiated cells is beneficial to the organism as a whole but disadvantageous from the point of view of individual cells, most of which lose the opportunity to reproduce themselves. In an asexual multicellular organism, rogue cells which retain the ability to reproduce may take over and reduce the organism to a mass of undifferentiated cells. Sexual reproduction eliminates such rogue cells from the next generation and therefore appears to be a prerequisite for complex multicellularity. [135]

The available evidence indicates that eukaryotes evolved much earlier but remained inconspicuous until a rapid diversification around 1 Ga. The only respect in which eukaryotes clearly surpass bacteria and archaea is their capacity for variety of forms, and sexual reproduction enabled eukaryotes to exploit that advantage by producing organisms with multiple cells that differed in form and function. [135]

By comparing the composition of transcription factor families and regulatory network motifs between unicellular organisms and multicellular organisms, scientists found there are many novel transcription factor families and three novel types of regulatory network motifs in multicellular organisms, and novel family transcription factors are preferentially wired into these novel network motifs which are essential for multicullular development. These results propose a plausible mechanism for the contribution of novel-family transcription factors and novel network motifs to the origin of multicellular organisms at transcriptional regulatory level. [136]

Fossil evidence Edit

The Francevillian biota fossils, dated to 2.1 Ga, are the earliest known fossil organisms that are clearly multicellular. [39] They may have had differentiated cells. [137] Another early multicellular fossil, Qingshania, dated to 1.7 Ga, appears to consist of virtually identical cells. The red algae called Bangiomorpha, dated at 1.2 Ga, is the earliest known organism that certainly has differentiated, specialized cells, and is also the oldest known sexually reproducing organism. [135] The 1.43 billion-year-old fossils interpreted as fungi appear to have been multicellular with differentiated cells. [115] The "string of beads" organism Horodyskia, found in rocks dated from 1.5 Ga to 900 Ma, may have been an early metazoan [21] however, it has also been interpreted as a colonial foraminiferan. [126]

Animals are multicellular eukaryotes, [note 1] and are distinguished from plants, algae, and fungi by lacking cell walls. [139] All animals are motile, [140] if only at certain life stages. All animals except sponges have bodies differentiated into separate tissues, including muscles, which move parts of the animal by contracting, and nerve tissue, which transmits and processes signals. [141] In November 2019, researchers reported the discovery of Caveasphaera, a multicellular organism found in 609-million-year-old rocks, that is not easily defined as an animal or non-animal, which may be related to one of the earliest instances of animal evolution. [142] [143] Fossil studies of Caveasphaera have suggested that animal-like embryonic development arose much earlier than the oldest clearly defined animal fossils. [142] and may be consistent with studies suggesting that animal evolution may have begun about 750 million years ago. [143] [144]

Nonetheless, the earliest widely accepted animal fossils are the rather modern-looking cnidarians (the group that includes jellyfish, sea anemones and Hydra), possibly from around 580 Ma , although fossils from the Doushantuo Formation can only be dated approximately. Their presence implies that the cnidarian and bilaterian lineages had already diverged. [145]

The Ediacara biota, which flourished for the last 40 million years before the start of the Cambrian, [146] were the first animals more than a very few centimetres long. Many were flat and had a "quilted" appearance, and seemed so strange that there was a proposal to classify them as a separate kingdom, Vendozoa. [147] Others, however, have been interpreted as early molluscs (Kimberella [148] [149] ), echinoderms (Arkarua [150] ), and arthropods (Spriggina, [151] Parvancorina [152] ). There is still debate about the classification of these specimens, mainly because the diagnostic features which allow taxonomists to classify more recent organisms, such as similarities to living organisms, are generally absent in the Ediacarans. However, there seems little doubt that Kimberella was at least a triploblastic bilaterian animal, in other words, an animal significantly more complex than the cnidarians. [153]

The small shelly fauna are a very mixed collection of fossils found between the Late Ediacaran and Middle Cambrian periods. The earliest, Cloudina, shows signs of successful defense against predation and may indicate the start of an evolutionary arms race. Some tiny Early Cambrian shells almost certainly belonged to molluscs, while the owners of some "armor plates," Halkieria and Microdictyon, were eventually identified when more complete specimens were found in Cambrian lagerstätten that preserved soft-bodied animals. [154]

In the 1970s there was already a debate about whether the emergence of the modern phyla was "explosive" or gradual but hidden by the shortage of Precambrian animal fossils. [154] A re-analysis of fossils from the Burgess Shale lagerstätte increased interest in the issue when it revealed animals, such as Opabinia, which did not fit into any known phylum. At the time these were interpreted as evidence that the modern phyla had evolved very rapidly in the Cambrian explosion and that the Burgess Shale's "weird wonders" showed that the Early Cambrian was a uniquely experimental period of animal evolution. [156] Later discoveries of similar animals and the development of new theoretical approaches led to the conclusion that many of the "weird wonders" were evolutionary "aunts" or "cousins" of modern groups [157] —for example that Opabinia was a member of the lobopods, a group which includes the ancestors of the arthropods, and that it may have been closely related to the modern tardigrades. [158] Nevertheless, there is still much debate about whether the Cambrian explosion was really explosive and, if so, how and why it happened and why it appears unique in the history of animals. [159]

Deuterostomes and the first vertebrates Edit

Most of the animals at the heart of the Cambrian explosion debate are protostomes, one of the two main groups of complex animals. The other major group, the deuterostomes, contains invertebrates such as starfish and sea urchins (echinoderms), as well as chordates (see below). Many echinoderms have hard calcite "shells," which are fairly common from the Early Cambrian small shelly fauna onwards. [154] Other deuterostome groups are soft-bodied, and most of the significant Cambrian deuterostome fossils come from the Chengjiang fauna, a lagerstätte in China. [161] The chordates are another major deuterostome group: animals with a distinct dorsal nerve cord. Chordates include soft-bodied invertebrates such as tunicates as well as vertebrates—animals with a backbone. While tunicate fossils predate the Cambrian explosion, [162] the Chengjiang fossils Haikouichthys and Myllokunmingia appear to be true vertebrates, [30] and Haikouichthys had distinct vertebrae, which may have been slightly mineralized. [163] Vertebrates with jaws, such as the acanthodians, first appeared in the Late Ordovician. [164]

Adaptation to life on land is a major challenge: all land organisms need to avoid drying-out and all those above microscopic size must create special structures to withstand gravity respiration and gas exchange systems have to change reproductive systems cannot depend on water to carry eggs and sperm towards each other. [165] [166] [167] Although the earliest good evidence of land plants and animals dates back to the Ordovician period ( 488 to 444 Ma ), and a number of microorganism lineages made it onto land much earlier, [168] [169] modern land ecosystems only appeared in the Late Devonian, about 385 to 359 Ma . [170] In May 2017, evidence of the earliest known life on land may have been found in 3.48-billion-year-old geyserite and other related mineral deposits (often found around hot springs and geysers) uncovered in the Pilbara Craton of Western Australia. [171] [172] In July 2018, scientists reported that the earliest life on land may have been bacteria living on land 3.22 billion years ago. [173] In May 2019, scientists reported the discovery of a fossilized fungus, named Ourasphaira giraldae, in the Canadian Arctic, that may have grown on land a billion years ago, well before plants were living on land. [174] [175] [176]

Evolution of terrestrial antioxidants Edit

Oxygen is a potent oxidant whose accumulation in terrestrial atmosphere resulted from the development of photosynthesis over 3 Ga, in cyanobacteria (blue-green algae), which were the most primitive oxygenic photosynthetic organisms. Brown algae accumulate inorganic mineral antioxidants such as rubidium, vanadium, zinc, iron, copper, molybdenum, selenium and iodine which is concentrated more than 30,000 times the concentration of this element in seawater. Protective endogenous antioxidant enzymes and exogenous dietary antioxidants helped to prevent oxidative damage. Most marine mineral antioxidants act in the cells as essential trace elements in redox and antioxidant metalloenzymes. [ citation needed ]

When plants and animals began to enter rivers and land about 500 Ma, environmental deficiency of these marine mineral antioxidants was a challenge to the evolution of terrestrial life. [177] [178] Terrestrial plants slowly optimized the production of “new” endogenous antioxidants such as ascorbic acid, polyphenols, flavonoids, tocopherols, etc. A few of these appeared more recently, in last 200–50 Ma, in fruits and flowers of angiosperm plants. [ citation needed ]

In fact, angiosperms (the dominant type of plant today) and most of their antioxidant pigments evolved during the Late Jurassic period. Plants employ antioxidants to defend their structures against reactive oxygen species produced during photosynthesis. Animals are exposed to the same oxidants, and they have evolved endogenous enzymatic antioxidant systems. [179] Iodine in the form of the iodide ion I- is the most primitive and abundant electron-rich essential element in the diet of marine and terrestrial organisms, and iodide acts as an electron donor and has this ancestral antioxidant function in all iodide-concentrating cells from primitive marine algae to more recent terrestrial vertebrates. [180]

Evolution of soil Edit

Before the colonization of land, soil, a combination of mineral particles and decomposed organic matter, did not exist. Land surfaces would have been either bare rock or unstable sand produced by weathering. Water and any nutrients in it would have drained away very quickly. [170] In the Sub-Cambrian peneplain in Sweden for example maximum depth of kaolinitization by Neoproterozoic weathering is about 5 m, in contrast nearby kaolin deposits developed in the Mesozoic are much thicker. [181] It has been argued that in the late Neoproterozoic sheet wash was a dominant process of erosion of surface material due to the lack of plants on land. [182]

Films of cyanobacteria, which are not plants but use the same photosynthesis mechanisms, have been found in modern deserts, and only in areas that are unsuitable for vascular plants. This suggests that microbial mats may have been the first organisms to colonize dry land, possibly in the Precambrian. Mat-forming cyanobacteria could have gradually evolved resistance to desiccation as they spread from the seas to intertidal zones and then to land. [170] Lichens, which are symbiotic combinations of a fungus (almost always an ascomycete) and one or more photosynthesizers (green algae or cyanobacteria), [183] are also important colonizers of lifeless environments, [170] and their ability to break down rocks contributes to soil formation in situations where plants cannot survive. [183] The earliest known ascomycete fossils date from 423 to 419 Ma in the Silurian. [170]

Soil formation would have been very slow until the appearance of burrowing animals, which mix the mineral and organic components of soil and whose feces are a major source of the organic components. [170] Burrows have been found in Ordovician sediments, and are attributed to annelids ("worms") or arthropods. [170] [184]

Plants and the Late Devonian wood crisis Edit

In aquatic algae, almost all cells are capable of photosynthesis and are nearly independent. Life on land required plants to become internally more complex and specialized: photosynthesis was most efficient at the top roots were required in order to extract water from the ground the parts in between became supports and transport systems for water and nutrients. [165] [185]

Spores of land plants, possibly rather like liverworts, have been found in Middle Ordovician rocks dated to about 476 Ma . In Middle Silurian rocks 430 Ma , there are fossils of actual plants including clubmosses such as Baragwanathia most were under 10 centimetres (3.9 in) high, and some appear closely related to vascular plants, the group that includes trees. [185]

By the Late Devonian 370 Ma , trees such as Archaeopteris were so abundant that they changed river systems from mostly braided to mostly meandering, because their roots bound the soil firmly. [186] In fact, they caused the "Late Devonian wood crisis" [187] because:

  • They removed more carbon dioxide from the atmosphere, reducing the greenhouse effect and thus causing an ice age in the Carboniferous period. [28] In later ecosystems the carbon dioxide "locked up" in wood is returned to the atmosphere by decomposition of dead wood. However, the earliest fossil evidence of fungi that can decompose wood also comes from the Late Devonian. [188]
  • The increasing depth of plants' roots led to more washing of nutrients into rivers and seas by rain. This caused algal blooms whose high consumption of oxygen caused anoxic events in deeper waters, increasing the extinction rate among deep-water animals. [28]

Land invertebrates Edit

Animals had to change their feeding and excretory systems, and most land animals developed internal fertilization of their eggs. [167] The difference in refractive index between water and air required changes in their eyes. On the other hand, in some ways movement and breathing became easier, and the better transmission of high-frequency sounds in air encouraged the development of hearing. [166]

The oldest known air-breathing animal is Pneumodesmus, an archipolypodan millipede from the Middle Silurian, about 428 Ma . [189] [190] Its air-breathing, terrestrial nature is evidenced by the presence of spiracles, the openings to tracheal systems. [191] However, some earlier trace fossils from the Cambrian-Ordovician boundary about 490 Ma are interpreted as the tracks of large amphibious arthropods on coastal sand dunes, and may have been made by euthycarcinoids, [192] which are thought to be evolutionary "aunts" of myriapods. [193] Other trace fossils from the Late Ordovician a little over 445 Ma probably represent land invertebrates, and there is clear evidence of numerous arthropods on coasts and alluvial plains shortly before the Silurian-Devonian boundary, about 415 Ma , including signs that some arthropods ate plants. [194] Arthropods were well pre-adapted to colonise land, because their existing jointed exoskeletons provided protection against desiccation, support against gravity and a means of locomotion that was not dependent on water. [167] [195]

The fossil record of other major invertebrate groups on land is poor: none at all for non-parasitic flatworms, nematodes or nemerteans some parasitic nematodes have been fossilized in amber annelid worm fossils are known from the Carboniferous, but they may still have been aquatic animals the earliest fossils of gastropods on land date from the Late Carboniferous, and this group may have had to wait until leaf litter became abundant enough to provide the moist conditions they need. [166]

The earliest confirmed fossils of flying insects date from the Late Carboniferous, but it is thought that insects developed the ability to fly in the Early Carboniferous or even Late Devonian. This gave them a wider range of ecological niches for feeding and breeding, and a means of escape from predators and from unfavorable changes in the environment. [196] About 99% of modern insect species fly or are descendants of flying species. [197]

Early land vertebrates Edit

Tetrapods, vertebrates with four limbs, evolved from other rhipidistian fish over a relatively short timespan during the Late Devonian ( 370 to 360 Ma ). [200] The early groups are grouped together as Labyrinthodontia. They retained aquatic, fry-like tadpoles, a system still seen in modern amphibians.

Iodine and T4/T3 stimulate the amphibian metamorphosis and the evolution of nervous systems transforming the aquatic, vegetarian tadpole into a "more evoluted" terrestrial, carnivorous frog with better neurological, visuospatial, olfactory and cognitive abilities for hunting. [177] The new hormonal action of T3 was made possible by the formation of T3-receptors in the cells of vertebrates. Firstly, about 600-500 million years ago, in primitive Chordata appeared the alpha T3-receptors with a metamorphosing action and then, about 250-150 million years ago, in the Birds and Mammalia appeared the beta T3-receptors with metabolic and thermogenetic actions. [201]

From the 1950s to the early 1980s it was thought that tetrapods evolved from fish that had already acquired the ability to crawl on land, possibly in order to go from a pool that was drying out to one that was deeper. However, in 1987, nearly complete fossils of Acanthostega from about 363 Ma showed that this Late Devonian transitional animal had legs and both lungs and gills, but could never have survived on land: its limbs and its wrist and ankle joints were too weak to bear its weight its ribs were too short to prevent its lungs from being squeezed flat by its weight its fish-like tail fin would have been damaged by dragging on the ground. The current hypothesis is that Acanthostega, which was about 1 metre (3.3 ft) long, was a wholly aquatic predator that hunted in shallow water. Its skeleton differed from that of most fish, in ways that enabled it to raise its head to breathe air while its body remained submerged, including: its jaws show modifications that would have enabled it to gulp air the bones at the back of its skull are locked together, providing strong attachment points for muscles that raised its head the head is not joined to the shoulder girdle and it has a distinct neck. [198]

The Devonian proliferation of land plants may help to explain why air breathing would have been an advantage: leaves falling into streams and rivers would have encouraged the growth of aquatic vegetation this would have attracted grazing invertebrates and small fish that preyed on them they would have been attractive prey but the environment was unsuitable for the big marine predatory fish air-breathing would have been necessary because these waters would have been short of oxygen, since warm water holds less dissolved oxygen than cooler marine water and since the decomposition of vegetation would have used some of the oxygen. [198]

Later discoveries revealed earlier transitional forms between Acanthostega and completely fish-like animals. [202] Unfortunately, there is then a gap (Romer's gap) of about 30 Ma between the fossils of ancestral tetrapods and Middle Carboniferous fossils of vertebrates that look well-adapted for life on land. Some of these look like early relatives of modern amphibians, most of which need to keep their skins moist and to lay their eggs in water, while others are accepted as early relatives of the amniotes, whose waterproof skin and egg membranes enable them to live and breed far from water. [199]

Dinosaurs, birds and mammals Edit

Anapsids whether turtles belong here is debated [203]

Amniotes, whose eggs can survive in dry environments, probably evolved in the Late Carboniferous period ( 330 to 298.9 Ma ). The earliest fossils of the two surviving amniote groups, synapsids and sauropsids, date from around 313 Ma . [204] [205] The synapsid pelycosaurs and their descendants the therapsids are the most common land vertebrates in the best-known Permian ( 298.9 to 251.902 Ma ) fossil beds. However, at the time these were all in temperate zones at middle latitudes, and there is evidence that hotter, drier environments nearer the Equator were dominated by sauropsids and amphibians. [206]

The Permian–Triassic extinction event wiped out almost all land vertebrates, [207] as well as the great majority of other life. [208] During the slow recovery from this catastrophe, estimated to have taken 30 million years, [209] a previously obscure sauropsid group became the most abundant and diverse terrestrial vertebrates: a few fossils of archosauriformes ("ruling lizard forms") have been found in Late Permian rocks, [210] but, by the Middle Triassic, archosaurs were the dominant land vertebrates. Dinosaurs distinguished themselves from other archosaurs in the Late Triassic, and became the dominant land vertebrates of the Jurassic and Cretaceous periods ( 201.3 to 66 Ma ). [211]

During the Late Jurassic, birds evolved from small, predatory theropod dinosaurs. [212] The first birds inherited teeth and long, bony tails from their dinosaur ancestors, [212] but some had developed horny, toothless beaks by the very Late Jurassic [213] and short pygostyle tails by the Early Cretaceous. [214]

While the archosaurs and dinosaurs were becoming more dominant in the Triassic, the mammaliaform successors of the therapsids evolved into small, mainly nocturnal insectivores. This ecological role may have promoted the evolution of mammals, for example nocturnal life may have accelerated the development of endothermy ("warm-bloodedness") and hair or fur. [215] By 195 Ma in the Early Jurassic there were animals that were very like today's mammals in a number of respects. [216] Unfortunately, there is a gap in the fossil record throughout the Middle Jurassic. [217] However, fossil teeth discovered in Madagascar indicate that the split between the lineage leading to monotremes and the one leading to other living mammals had occurred by 167 Ma . [218] After dominating land vertebrate niches for about 150 Ma, the non-avian dinosaurs perished in the Cretaceous–Paleogene extinction event ( 66 Ma ) along with many other groups of organisms. [219] Mammals throughout the time of the dinosaurs had been restricted to a narrow range of taxa, sizes and shapes, but increased rapidly in size and diversity after the extinction, [220] [221] with bats taking to the air within 13 million years, [222] and cetaceans to the sea within 15 million years. [223]

Flowering plants Edit

The first flowering plants appeared around 130 Ma. [226] The 250,000 to 400,000 species of flowering plants outnumber all other ground plants combined, and are the dominant vegetation in most terrestrial ecosystems. There is fossil evidence that flowering plants diversified rapidly in the Early Cretaceous, from 130 to 90 Ma , [224] [225] and that their rise was associated with that of pollinating insects. [225] Among modern flowering plants Magnolia are thought to be close to the common ancestor of the group. [224] However, paleontologists have not succeeded in identifying the earliest stages in the evolution of flowering plants. [224] [225]

Social insects Edit

The social insects are remarkable because the great majority of individuals in each colony are sterile. This appears contrary to basic concepts of evolution such as natural selection and the selfish gene. In fact, there are very few eusocial insect species: only 15 out of approximately 2,600 living families of insects contain eusocial species, and it seems that eusociality has evolved independently only 12 times among arthropods, although some eusocial lineages have diversified into several families. Nevertheless, social insects have been spectacularly successful for example although ants and termites account for only about 2% of known insect species, they form over 50% of the total mass of insects. Their ability to control a territory appears to be the foundation of their success. [227]

The sacrifice of breeding opportunities by most individuals has long been explained as a consequence of these species' unusual haplodiploid method of sex determination, which has the paradoxical consequence that two sterile worker daughters of the same queen share more genes with each other than they would with their offspring if they could breed. [228] However, E. O. Wilson and Bert Hölldobler argue that this explanation is faulty: for example, it is based on kin selection, but there is no evidence of nepotism in colonies that have multiple queens. Instead, they write, eusociality evolves only in species that are under strong pressure from predators and competitors, but in environments where it is possible to build "fortresses" after colonies have established this security, they gain other advantages through co-operative foraging. In support of this explanation they cite the appearance of eusociality in bathyergid mole rats, [227] which are not haplodiploid. [229]

The earliest fossils of insects have been found in Early Devonian rocks from about 400 Ma , which preserve only a few varieties of flightless insect. The Mazon Creek lagerstätten from the Late Carboniferous, about 300 Ma , include about 200 species, some gigantic by modern standards, and indicate that insects had occupied their main modern ecological niches as herbivores, detritivores and insectivores. Social termites and ants first appear in the Early Cretaceous, and advanced social bees have been found in Late Cretaceous rocks but did not become abundant until the Middle Cenozoic. [230]

Humans Edit

The idea that, along with other life forms, modern-day humans evolved from an ancient, common ancestor was proposed by Robert Chambers in 1844 and taken up by Charles Darwin in 1871. [231] Modern humans evolved from a lineage of upright-walking apes that has been traced back over 6 Ma to Sahelanthropus. [232] The first known stone tools were made about 2.5 Ma , apparently by Australopithecus garhi, and were found near animal bones that bear scratches made by these tools. [233] The earliest hominines had chimpanzee-sized brains, but there has been a fourfold increase in the last 3 Ma a statistical analysis suggests that hominine brain sizes depend almost completely on the date of the fossils, while the species to which they are assigned has only slight influence. [234] There is a long-running debate about whether modern humans evolved all over the world simultaneously from existing advanced hominines or are descendants of a single small population in Africa, which then migrated all over the world less than 200,000 years ago and replaced previous hominine species. [235] There is also debate about whether anatomically modern humans had an intellectual, cultural and technological "Great Leap Forward" under 100,000 years ago and, if so, whether this was due to neurological changes that are not visible in fossils. [236]

Life on Earth has suffered occasional mass extinctions at least since 542 Ma . Although they were disasters at the time, mass extinctions have sometimes accelerated the evolution of life on Earth. When dominance of particular ecological niches passes from one group of organisms to another, it is rarely because the new dominant group is "superior" to the old and usually because an extinction event eliminates the old dominant group and makes way for the new one. [37] [237]

The fossil record appears to show that the gaps between mass extinctions are becoming longer and the average and background rates of extinction are decreasing. Both of these phenomena could be explained in one or more ways: [238]

  • The oceans may have become more hospitable to life over the last 500 Ma and less vulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greater depths the development of life on land reduced the run-off of nutrients and hence the risk of eutrophication and anoxic events and marine ecosystems became more diversified so that food chains were less likely to be disrupted. [239][240]
  • Reasonably complete fossils are very rare, most extinct organisms are represented only by partial fossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different genera, which were often defined solely to accommodate these finds—the story of Anomalocaris is an example of this. The risk of this mistake is higher for older fossils because these are often both unlike parts of any living organism and poorly conserved. Many of the "superfluous" genera are represented by fragments which are not found again and the "superfluous" genera appear to become extinct very quickly. [238]

Biodiversity in the fossil record, which is ". the number of distinct genera alive at any given time that is, those whose first occurrence predates and whose last occurrence postdates that time" [241] shows a different trend: a fairly swift rise from 542 to 400 Ma a slight decline from 400 to 200 Ma , in which the devastating Permian–Triassic extinction event is an important factor and a swift rise from 200 Ma to the present. [241]

Approximately how long do bacteria live for? - Biology

Bacteria are tiny, one-celled organisms – generally 4/100,000 of an inch wide (1 µm) and somewhat longer in length. What bacteria lack in size, they make up in numbers. A teaspoon of productive soil generally contains between 100 million and 1 billion bacteria. That is as much mass as two cows per acre.

Bacteria fall into four functional groups. Most are decomposers that consume simple carbon compounds, such as root exudates and fresh plant litter. By this process, bacteria convert energy in soil organic matter into forms useful to the rest of the organisms in the soil food web. A number of decomposers can break down pesticides and pollutants in soil. Decomposers are especially important in immobilizing, or retaining, nutrients in their cells, thus preventing the loss of nutrients, such as nitrogen, from the rooting zone.

A second group of bacteria are the mutualists that form partnerships with plants. The most well-known of these are the nitrogen-fixing bacteria. The third group of bacteria is the pathogens. Bacterial pathogens include Xymomonas and Erwinia species, and species of Agrobacterium that cause gall formation in plants. A fourth group, called lithotrophs or chemoautotrophs, obtains its energy from compounds of nitrogen, sulfur, iron or hydrogen instead of from carbon compounds. Some of these species are important to nitrogen cycling and degradation of pollutants.


Bacteria from all four groups perform important services related to water dynamics, nutrient cycling, and disease suppression. Some bacteria affect water movement by producing substances that help bind soil particles into small aggregates (those with diameters of 1/10,000-1/100 of an inch or 2-200µm). Stable aggregates improve water infiltration and the soil’s water-holding ability. In a diverse bacterial community, many organisms will compete with disease-causing organisms in roots and on aboveground surfaces of plants.


Nitrogen-fixing bacteria form symbiotic associations with the roots of legumes like clover and lupine, and trees such as alder and locust. Visible nodules are created where bacteria infect a growing root hair (Figure 4). The plant supplies simple carbon compounds to the bacteria, and the bacteria convert nitrogen (N2) from air into a form the plant host can use. When leaves or roots from the host plant decompose, soil nitrogen increases in the surrounding area.

Nitrifying bacteria change ammonium (NH4+) to nitrite (NO2-) then to nitrate (NO3-) – a preferred form of nitrogen for grasses and most row crops. Nitrate is leached more easily from the soil, so some farmers use nitrification inhibitors to reduce the activity of one type of nitrifying bacteria. Nitrifying bacteria are suppressed in forest soils, so that most of the nitrogen remains as ammonium.

Denitrifying bacteria convert nitrate to nitrogen (N2) or nitrous oxide (N2O) gas. Denitrifiers are anaerobic, meaning they are active where oxygen is absent, such as in saturated soils or inside soil aggregates.

Actinomycetes are a large group of bacteria that grow as hyphae like fungi (Figure 3). They are responsible for the characteristically “earthy” smell of freshly turned, healthy soil. Actinomycetes decompose a wide array of substrates, but are especially important in degrading recalcitrant (hard-to-decompose) compounds, such as chitin and cellulose, and are active at high pH levels. Fungi are more important in degrading these compounds at low pH. A number of antibiotics are produced by actinomycetes such as Streptomyces.


Various species of bacteria thrive on different food sources and in different microenvironments. In general, bacteria are more competitive when labile (easy-to-metabolize) substrates are present. This includes fresh, young plant residue and the compounds found near living roots. Bacteria are especially concentrated in the rhizosphere, the narrow region next to and in the root. There is evidence that plants produce certain types of root exudates to encourage the growth of protective bacteria.

Bacteria alter the soil environment to the extent that the soil environment will favor certain plant communities over others. Before plants can become established on fresh sediments, the bacterial community must establish first, starting with photosynthetic bacteria. These fix atmospheric nitrogen and carbon, produce organic matter, and immobilize enough nitrogen and other nutrients to initiate nitrogen cycling processes in the young soil. Then, early successional plant species can grow. As the plant community is established, different types of organic matter enter the soil and change the type of food available to bacteria. In turn, the altered bacterial community changes soil structure and the environment for plants. Some researchers think it may be possible to control the plant species in a place by managing the soil bacteria community.

By Ann Kennedy, USDA Agricultural Research Service, Pullman, WA

Bacteria That Promote Plant Growth: Certain strains of the soil bacteria Pseudomonas fluorescens have anti-fungal activity that inhibits some plant pathogens. P. fluorescens and other Pseudomonas and Xanthomonas species can increase plant growth in several ways. They may produce a compound that inhibits the growth of pathogens or reduces invasion of the plant by a pathogen. They may also produce compounds (growth factors) that directly increase plant growth.

These plant growth-enhancing bacteria occur naturally in soils, but not always in high enough numbers to have a dramatic effect. In the future, farmers may be able to inoculate seeds with anti-fungal bacteria, such as P. fluorescens, to ensure that the bacteria reduce pathogens around the seed and root of the crop.

We are living in a bacterial world, and it's impacting us more than previously thought

The percentage of the human genome that arose at a series of stages in evolution. 37% of human genes originated in bacteria. Credit: Margaret McFall-Ngai, et al. ©2013 PNAS

(—Throughout her career, the famous biologist Lynn Margulis (1938-2011) argued that the world of microorganisms has a much larger impact on the entire biosphere—the world of all living things—than scientists typically recognize. Now a team of scientists from universities around the world has collected and compiled the results of hundreds of studies, most from within the past decade, on animal-bacterial interactions, and have shown that Margulis was right. The combined results suggest that the evidence supporting Margulis' view has reached a tipping point, demanding that scientists reexamine some of the fundamental features of life through the lens of the complex, codependent relationships among bacteria and other very different life forms.

The project to review the current research on animal-bacterial interactions began when some scientists recognized the importance of bacteria in their own fields of study. For Michael Hadfield, Professor of Biology at the University of Hawaii at Manoa, the recognition grew over many years while studying the metamorphosis of marine animals. He found that certain bacteria influence marine larvae to settle to particular places on the sea floor, where they transform into juveniles and live out the rest of their lives.

"Once we determined that specific biofilm bacteria provide an essential and unique ligand to stimulate the larvae of one globally distributed marine worm, our research naturally progressed to a study of the portion of the bacterial genome responsible for the signaling, and to other species, where we found the same genes involved," Hadfield told "Coming from different perspectives on the study of animal-bacterial interactions, and recognizing many more, Margaret McFall-Ngai [Professor of Medical Microbiology and Immunology at the University of Wisconsin, Madison] and I discussed the current situation extensively and then decided to attempt to draw together a significant number of experts on various approaches to the study of bacterial-animal interactions to draft a paper such as the one you have in hand. We proposed a 'catalysis meeting' on the subject to the National Science Foundation's National Evolutionary Synthesis Center (NESCent), which was funded, and the project took off."

In many respects, it's easy to see the prominent role that bacteria play in the world. Bacteria were one of the first life forms to appear on Earth, about 3.8 billion years ago, and they will most likely survive long after humans are gone. In the current tree of life, they occupy one of the three main branches (the other two are Archaea and Eucarya, with animals belonging to the latter). Although bacteria are extremely diverse and live nearly everywhere on Earth, from the bottom of the ocean to the inside of our intestines, they have a few things in common. They are similar in size (a few micrometers), they are usually made of either a single cell or a few cells, and their cells don't have nuclei.

Although scientists have known for many years that animals serve as a host for bacteria, which live especially in the gut/intestines, in the mouth, and on the skin, recent research has uncovered just how numerous these microbes are. Studies have shown that humans have about 10 times more bacterial cells in our bodies than we have human cells. (However, the total bacteria weigh less than half a pound because bacterial cells are much smaller than human cells.)

While some of these bacteria simply live side-by-side with animals, not interacting much, some of them interact a lot. We often associate bacteria with disease-causing "germs" or pathogens, and bacteria are responsible for many diseases, such as tuberculosis, bubonic plague, and MRSA infections. But bacteria do many good things, too, and the recent research underlines the fact that animal life would not be the same without them.

"The true number of bacterial species in the world is staggeringly huge, including bacteria now found circling the Earth in the most upper layers of our atmosphere and in the rocks deep below the sea floor," Hadfield said. "Then add all of those from all of the possible environments you can think of, from cesspools to hot springs, and all over on and in virtually every living organism. Therefore, the proportion of all bacterial species that is pathogenic to plants and animals is surely small. I suspect that the proportion that is beneficial/necessary to plants and animals is likewise small relative to the total number of bacteria present in the universe, and surely most bacteria, in this perspective, are 'neutral.' However, I am also convinced that the number of beneficial microbes, even very necessary microbes, is much, much greater than the number of pathogens."

Animal origins and coevolution

From our humble beginnings, bacteria may have played an important role by assisting in the origins of multicellular organisms (about 1-2 billion years ago) and in the origins of animals (about 700 million years ago). Researchers have recently discovered that one of the closest living relatives of multicellular animals, a single-celled choanoflagellate, responds to signals from one of its prey bacterium. These signals cause dividing choanoflagellate cells to retain connections, leading to the formation of well-coordinated colonies that may have become multicellular organisms. However, such questions of origin have been subjects of intense debate, and scientists have many hypotheses about how these life forms emerged. A bacterial role in these processes does not exclude other perspectives but adds an additional consideration.

Bacteria in an animal’s microbiota, such as those in the gut, in the mouth, and on the skin, communicate among themselves and exchange signals with the animal’s organ systems. Some of the chemical signals are noted in this illustration. Credit: Margaret McFall-Ngai, et al. ©2013 PNAS

After helping get animals started, bacteria also played an important role in helping them along their evolutionary path. While animal development is traditionally thought to be directed primarily by the animal's own genome in response to environmental factors, recent research has shown that animal development may be better thought of as an orchestration among the animal, the environment, and the coevolution of numerous microbial species. One example of this coevolution may have occurred when mammals evolved endothermy, or the ability to maintain a constant temperature of approximately 40 °C (100 °F) by metabolic means. This is also the temperature at which mammals' bacterial partners work at optimum efficiency, providing energy for the mammals and reducing their food requirement. This finding suggests that bacteria's preferred temperature may have placed a selection pressure on the evolution of genes associated with endothermy.

Evidence for a deep-rooted alliance between animals and bacteria also emerges in both groups' genomes. Researchers estimate that about 37% of the 23,000 human genes have homologs with bacteria and Archaea, i.e., they are related to genes found in bacteria and Archaea that were derived from a common ancestor.

Many of these homologous genes enable signaling between animals and bacteria, which suggests that they have been able to communicate and influence each other's development. One example is Hadfield and his group's discovery that bacterial signaling plays an essential role in inducing metamorphosis in some marine invertebrate larvae, where the bacteria produce cues associated with particular environmental factors. Other studies have found that bacterial signaling influences normal brain development in mammals, affects reproductive behavior in both vertebrates and invertebrates, and activates the immune system in tsetse flies. The olfactory chemicals that attract some animals (including humans) to their prospective mates are also produced by the animals' resident bacteria.

Bacterial signaling is not only essential for development, it also helps animals maintain homeostasis, keeping us healthy and happy. As research has shown, bacteria in the gut can communicate with the brain through the central nervous system. Studies have found that mice without certain bacteria have defects in brain regions that control anxiety and depression-like behavior. Bacterial signaling also plays an essential role in guarding an animal's immune system. Disturbing these bacterial signaling pathways can lead to diseases such as diabetes, inflammatory bowel disease, and infections. Studies also suggest that many of the pathogens that cause disease in animals have "hijacked" these bacterial communication channels that originally evolved to maintain a balance between the animal and hundreds of beneficial bacterial species.

Signaling also appears in the larger arena of ecosystems. For example, bacteria in flower nectar can change the chemical properties of the nectar, influencing the way pollinators interact with plants. Human infants who are born vaginally have different gut bacteria than those delivered by Caesarean section, which may have long-lasting effects. And bacteria feeding on dead animals can repel animal scavengers—organisms 10,000 times their size—by producing noxious odors that signal the scavengers to stay away.

In the earliest animals, gut bacteria played an important role in nutrition by helping animals digest their food, and may have influenced the development of other nearby organ systems, such as the respiratory and urogenital systems. Likewise, animal evolution likely drove the evolution of the bacteria, sometimes into highly specialized niches. For example, 90% of the bacterial species in termite guts are not found anywhere else. Such specialization also means that the extinction of every animal species results in the extinction of an unknown number of bacterial lineages that have evolved along with it.

Scientists have also discovered that bacteria in the human gut adapts to changing diets. For example, most Americans have a gut microbiome that is optimized for digesting a high-fat, high-protein diet, while people in rural Amazonas, Venezuela, have gut microbes better suited for breaking down complex carbohydrates. Some people in Japan even have a gut bacterium that can digest seaweed. Researchers think the gut microbiome adapts in two ways: by adding or removing certain bacteria species, and by transferring the desired genes from one bacterium to another through horizontal gene transfer. Both host and bacteria benefit from this kind of symbiotic relationship, which researchers think is much more widespread than previously thought.

Altogether, the recent studies have shown that animals and bacteria have histories that are deeply intertwined, and depend on each other for their own health and well-being as well as that of their environments. Although the researchers focused exclusively on animal-bacteria interactions, they expect that similar trends of codependency and symbiosis are universal among and between other groups, such as Archaea, fungi, plants, and animals. Once considered an exception, such intermingling is now becoming recognized as the rule—just as Margulis predicted many decades ago. Due to these symbiotic relationships, the scientists here propose that the very definitions of an organism, an environment, a population, and a genome have become blurred and should be reviewed. It may be, for instance, that animals are better viewed as host-microbe ecosystems than as individuals.

An insect (1 mm) living in a forest canopy (10 m) illustrates the effects animal-bacterial interactions across multiple scales. Bacteria (1 micrometer) residing in the animal’s gut (0.1 mm) are essential to the insect’s nutrition, and insects often make up a majority of the animal biomass in forest canopies. Credit: Margaret McFall-Ngai, et al. ©2013 PNAS

In addition, the scientists predict that the recent findings on animal-bacteria interactions will likely require biologists to significantly alter their view of the fundamental nature of the entire biosphere. Along these lines, large-scale research projects such as the Human Microbiome Project and the Earth Microbiome Project are already underway to investigate the wide range of bacteria in the individual and global systems, and to see what happens when the bacteria are disturbed.

In the end, the scientists hope that the results will promote more cross-disciplinary collaboration among scientists and engineers from different fields to explore the new microbial frontier. They argue that these discoveries should revolutionize the way that biology is taught from the high school level on up, by focusing more on the relationships between bacteria, their animal partners, and all other life forms.

"It is hard to summarize a single 'most important conclusion,' other than the admonition to biologists studying animals, from behavior to physiology and ecology to molecular biology, that no matter what process you think you are studying, you must look for and consider a major role for bacteria," Hadfield said. "In many cases, this may require partnerships across traditional boundaries of research, meaning that zoologists must collaborate with microbiologists to advance their research, that molecular biologists must collaborate with whole-organism biologists, etc. We want badly for the message in 'Animals in a bacterial world,' to be a call for the necessary disappearance of the old boundaries between life science departments (e.g., Depts of Zoology, Botany, Microbiology, etc.) in universities, and societies (e.g., the American Society for Microbiology, etc.). We also want the message disseminated in college and university classes from introductory biology to advanced courses in the various topic areas of our paper."

The results will profoundly change the way that the scientists of this collaboration continue with their own areas of research, Hadfield said.

"Each of the authors of our paper conducts basic research in one or more areas of animal-bacterial interactions discussed in the paper, and each will continue to focus on her/his own speciality, I'm sure," he said. "However, I'm also certain that the interactions developed during the composition and writing of the paper (starting with our NESCent meeting in October 2011, when most of us met for the first time) will impact our own research and cause us to establish new collaborations with other laboratories. That has already occurred for me I have a new collaboration with Dianne Newman's group at CalTech, an outstanding group of bacteriologists who are helping us do a much more in-depth investigation of the bacterial gene-products responsible for larval development."

How bacteria colonize the human gut – study reveals important insights

Our bodies are hosts to some hundreds of thousands of bacteria that live in harmony with each other, helping the body be healthy, in return for the food and shelter it provides to these tiny organisms . Collectively, all the microorganisms inside the human body are referred to as the microbiome, most of whom are found in the gastrointestinal (GI) tract – in particular, the colon. Scientists have known for many years that the bacteria inside our bodies are indispensable for human health, but what has always bothered them is a pestering puzzle that until recently has remained largely unsolved. Considering the gut is such a flexible system where food, fecal matter and other fluids are constantly interchanged, how do bacteria thrive in such a system – namely, how do they manage stable microbial colonization of the gut?

A recent study performed by researchers at California Institute of Technology (Caltech), led biologist Sarkis Mazmanian, may have finally come up with an answer. After studying one common group of bacteria, the scientists found evidence that a set of genes is paramount to gut colonization. In addition, the Caltech researchers also found out that the bacteria, some of them at least, are in direct contact with the host body – something that was unperceivable until of late. These advances in our understanding of how the bacteria inside the gut work and flourish might help scientists devise ways to correct for abnormal changes in bacterial communities—changes that are thought to be connected to disorders like obesity, inflammatory bowel disease and autism.

Colonizing the human gut

A section of mouse colon is shown with gut bacteria (outlined in yellow) residing within the crypt channel.
Credit: Caltech / Mazmanian Lab

The focus of the researchers’ experiments was on a genus of microbes called Bacteriodes, a group of bacteria that has several dozen species and which can be found in the greatest abundance in the human microbiome. Bacteriodes wasn’t chosen because of its popularity, however, instead because it also makes for an excellent lab pet – it can be cultured in the lab (unlike most gut bacteria), and can be genetically modified to introduce specific mutations, fundamental criteria in order to test what effects and consequences these bacteria pose in the human body.

A few different species of the bacteria were added to one mouse, which was sterile (germ-free), to see if they would compete with each other to colonize the gut. They appeared to peacefully coexist, as expected, but then the researchers first colonized a mouse with one particular species, Bacteroides fragilis, and inoculated the mouse with the same exact species as in the first instance, to see if they would co-colonize the same host. To the researchers’ surprise, the newly introduced bacteria could not maintain residence in the mouse’s gut, despite the fact that the animal was already populated by the identical species.

“We know that this environment can house hundreds of species, so why the competition within the same species?” says Lead author S. Melanie Lee (PhD 󈧑), who was an MD/PhD student in Mazmanian’s lab at the time of the research. “There certainly isn’t a lack of space or nutrients, but this was an extremely robust and consistent finding when we tried to essentially ‘super-colonize’ the mice with one species.”

To explain the results, Lee and the team developed what they called the “saturable niche hypothesis.” The idea is that by saturating a specific habitat, the organism will effectively exclude others of the same species from occupying that niche. It will not, however, prevent other closely related species from colonizing the gut, because they have their own particular niches. A genetic screen revealed a set of previously uncharacterized genes—a system that the researchers dubbed commensal colonization factors (CCF)—that were both required and sufficient for species-specific colonization by B. fragilis.

“Melanie hypothesized that this saturable niche was part of the host tissue”—that is, of the gut itself—Mazmanian says. “When she postulated this three to four years ago, it was absolute heresy, because other researchers in the field believed that all bacteria in our intestines lived in the lumen—the center of the gut—and made zero contact with the host…our bodies. The rationale behind this thinking was if bacteria did make contact, it would cause some sort of immune response.”

“We are not alone…”

Upon using advanced imaging techniques and technology to survey colonic tissue in B. fragilis colonized mice, the researchers found a small population of microbes living in tiny pockets called crypts. The discovery is extremely important because it explains how the bacteria protect themselves from the constant flow of matter that passes through the GI tract. An even more important discovery came later on. In order to test if these CCF genes had anything to do with how the bacteria colonize the crypts that shelter them from harm, the researchers injected mutant bacteria (without CCF) into the colons of sterile mice. Those bacteria couldn’t colonize the crypts, proving they’re indispensable to the colonization mechanism of gut bacteria.

“There is something in that crypt—and we don’t know what it is yet—that normal B. fragilis can use to get a foothold via the CCF system,” Mazmanian explains. “Finding the crypts is a huge advance in the field because it shows that bacteria do physically contact the host. And during all of the experiments that Melanie did, homeostasis, or a steady state, was maintained. So, contrary to popular belief, there was no evidence of inflammation as a result of the bacteria contacting the host. In fact, we believe these crypts are the permanent home of Bacteroides, and perhaps other classes of microbes.”

The discovery doesn’t however explain however how other bacteria colonize the gut, considering they don’t have CCF genes at all. A hypothesis proposed by the Caltech researchers is that Bacteroides are keystone species—a necessary factor for building the gut ecosystem.

“This research highlights the notion that we are not alone. We knew that bacteria are in our gut, but this study shows that specific microbes are very intimately associated with our bodies,” Mazmanian says. “They are living in very close proximity to our tissues, and we can’t ignore microbial contributions to our biology or our health. They are a part of us.”

Approximately how long do bacteria live for? - Biology

Overview Of Bacteriology (page 1)

The Bacteria are a group of single-cell microorganisms with procaryotic cellular configuration. The genetic material (DNA) of procaryotic cells exists unbound in the cytoplasm of the cells. There is no nuclear membrane, which is the definitive characteristic of eucaryotic cells such as those that make up, fungi, protista, plants and animals. Until recently, bacteria were the only known type of procaryotic cell, and the discipline of biology related to their study is called bacteriology. In the 1980's, with the outbreak of molecular techniques applied to phylogeny of life, another group of procaryotes was defined and informally named "archaebacteria". This group of procaryotes has since been renamed Archaea and has been awarded biological Domain status on the level with Bacteria and Eucarya. The current science of bacteriology includes the study of both domains of procaryotic cells, but the name "bacteriology" is not likely to change to reflect the inclusion of archaea in the discipline. Actually, many archaea have been studied as intensively and as long as their bacterial counterparts, except with the notion that they were bacteria.

Figure 1. The cyanobacterium Anabaena. American Society for Microbiology. Two (not uncommon) exceptions that procaryotes are unicellular and undifferentiated are seen in Anabaena: 1. The organism lives as a multicellular filament or chain of cells. Procaryotes are considered "unicellular organisms" because all the cells in a filament or colony are of the same type, and any one individual cell can give rise to an exact filament or colony 2. The predominant photosynthetic (bright yellow-green) cells do differentiate into another type of cell: the obviously large "empty" cells occasionally seen along a filament are differentiated cells in which nitrogen fixation, but not photosynthesis, takes place.

When life arose on Earth about 4 billion years ago, the first types of cells to evolve were procaryotic cells. For approximately 2 billion years, procaryotic-type cells were the only form of life on Earth. The oldest known sedimentary rocks, from Greenland, are about 3.8 billion years old. The oldest known fossils are procaryotic cells, 3.5 billion years in age, found in Western Australia and South Africa. The nature of these fossils, and the chemical composition of the rocks in which they are found, indicates that lithotrophic and fermentative modes of metabolism were the first to evolve in early procaryotes. Photosynthesis developed in bacteria a bit later, at least 3 billion years ago. Anoxygenic photosynthesis (bacterial photosynthesis, which is anaerobic and does not produce O2) preceded oxygenic photosynthesis (plant-type photosynthesis, which yields O2). However, oxygenic photosynthesis also arose in procaryotes, specifically in the cyanobacteria, which existed millions of years before the evolution of green algae and plants. Larger, more complicated eucaryotic cells did not appear until much later, between 1.5 and 2 billion years ago.

Figure 2. Opalescent Pool in Yellowstone National Park, Wyoming USA. K. Todar. Conditions for life in this environment are similar to Earth over 2 billion years ago. In these types of hot springs, the orange, yellow and brown colors are due to pigmented photosynthetic bacteria which make up the microbial mats. The mats are literally teeming with bacteria. Some of these bacteria such as Synechococcus conduct oxygenic photosynthesis, while others such as Chloroflexus conduct anoxygenic photosynthesis. Other non-photosynthetic bacteria, as well as thermophilic and acidophilic Archaea, are also residents of the hot spring community.

The archaea and bacteria differ fundamentally in their structure from eucaryotic cells, which always contain a membrane-enclosed nucleus, multiple chromosomes, and various other membranous organelles such as mitochondria, chloroplasts, the golgi apparatus, vacuoles, etc. Unlike plants and animals, archaea and bacteria are unicellular organisms that do not develop or differentiate into multicellular forms. Some bacteria grow in filaments or masses of cells, but each cell in the colony is identical and capable of independent existence. The cells may be adjacent to one another because they did not separate after cell division or because they remained enclosed in a common sheath or slime secreted by the cells, but typically there is no continuity or communication between the cells.

The Universal Tree of Life

On the basis of small subunit ribosomal RNA (ssrRNA) analysis, the contemporary Tree of Life gives rise to three cellular "Domains": Archaea, Bacteria, and Eucarya (Figure 3). Bacteria (formerly known as eubacteria) and Archaea (formerly called archaebacteria) share the procaryotic type of cellular configuration, but otherwise are not related to one another any more closely than they are to the eucaryotic domain, Eucarya. Between the two procaryotes, Archaea are apparently more closely related to Eucarya than are the Bacteria. Eucarya consists of all eucaryotic cell-types, including protista, fungi, plants and animals.

Figure 3. The Universal Tree of Life as derived from sequencing of ssrRNA. N. Pace. Note the three major domains of living organisms: Archaea, Bacteria and Eucarya. The "evolutionary distance" between two organisms is proportional to the measurable distance between the end of a branch to a node to the end of a comparative branch. For example, in Eucarya, humans (Homo) are more closely related to corn (Zea) than to slime molds (Dictyostelium) or in Bacteria, E. coli is more closely related to Agrobacterium than to Thermus.

Size and Distribution of Bacteria and Archaea

Most procaryotic cells are very small compared to eucaryotic cells. A typical bacterial cell is about 1 micrometer in diameter or width, while most eucaryotic cells are from 10 to 100 micrometers in diameter. Eucaryotic cells have a much greater volume of cytoplasm and a much lower surface: volume ratio than procaryotic cells. A typical procaryotic cell is about the size of a eucaryotic mitochondrion. Since procaryotes are too small to be seen except with the aid of a microscope, it is usually not appreciated that they are the most abundant form of life on the planet, both in terms of biomass and total numbers of species. For example, in the sea, procaryotes make up 90 percent of the total combined weight of all organisms. In a single gram of fertile agricultural soil there may be in excess of 10 9 bacterial cells, outnumbering all eucaryotic cells there by 10,000 : 1. About 3,000 distinct species of bacteria and archaea are recognized, but this number is probably less than one percent of all the species in nature. These unknown procaryotes, far in excess of undiscovered or unstudied plants, are a tremendous reserve of genetic material and genetic information in nature that awaits exploitation.

Procaryotes are found in all of the habitats where eucaryotes live, but, as well, in many natural environments considered too extreme or inhospitable for eucaryotic cells. Thus, the outer limits of life on Earth (hottest, coldest, driest, etc.) are usually defined by the existence of procaryotes. Where eucaryotes and procaryotes live together, there may be mutualistic associations between the organisms that allow both to survive or flourish. The organelles of eucaryotes (mitochondria and chloroplasts) are thought to be remnants of Bacteria that invaded, or were captured by, primitive eucaryotes in the evolutionary past. Numerous types of eucaryotic cells that exist today are inhabited by endosymbiotic procaryotes.

From a metabolic standpoint, the procaryotes are extraordinarily diverse, and they exhibit several types of metabolism that are rarely or never seen in eucaryotes. For example, the biological processes of nitrogen fixation (conversion of atmospheric nitrogen gas to ammonia) and methanogenesis (production of methane) are metabolically-unique to procaryotes and have an enormous impact on the nitrogen and carbon cycles in nature. Unique mechanisms for energy production and photosynthesis are also seen among the Archaea and Bacteria.

The lives of plants and animals are dependent upon the activities of bacterial cells. Bacteria and archaea enter into various types of symbiotic relationships with plants and animals that usually benefit both organisms, although a few bacteria are agents of disease.

The metabolic activities of procaryotes in soil habitats have an enormous impact on soil fertility that can affect agricultural practices and crop yields. In the global environment, procaryotes are absolutely essential to drive the cycles of elements that make up living systems, i.e., the carbon, oxygen, nitrogen and sulfur cycles. The origins of the plant cell chloroplast and plant-type (oxygenic) photosynthesis are found in procaryotes. Most of the earth's atmospheric oxygen may have been produced by free-living bacterial cells. The bacteria fix nitrogen and a substantial amount of CO2, as well.

Bacteria or bacterial products (including their genes) can be used to increase crop yield or plant resistance to disease, or to cure or prevent plant disease. Bacterial products include antibiotics to fight infectious disease, as well as components for vaccines used to prevent infectious disease. Because of their simplicity and our relative understanding of their biological processes, the bacteria provide convenient laboratory models for study of the molecular biology, genetics, and physiology of all types of cells, including plant and animal cells.

How Long do Fossils Take to Form? –by Raul Esperante

Fossils are a record of organisms that lived in the past. are two main categories of fossils: body fossils and ichnofossils. Body fossils are the result of preservation of parts or the entire body of a plant, animal, or microorganism. These are the fossils that people are most familiar with, consisting of skeletons, teeth, shells, carapaces, organisms in amber, petrified wood, plant material, pollen, etc. Ichnofossils (also called trace fossils) are evidence of an organism&rsquos activity. Common ichnofossils are animal footprints and trackways, burrows, traces of plant roots, coprolites (fossil feces), and borings in rocks, bones, wood, shells, or other substrates. The study of fossils provides information about ancient biological communities, and the physiology, behavior, and ecology of organisms.

Fossils are mostly found in sedimentary rocks, which are formed by deposition of sand and mud, or precipitation of minerals like calcite and silica. Most sedimentary rocks and the fossils therein contain evidence of aquatic deposition. The study of the fossils and the associated rocks in which they are preserved gives us information about ancient conditions in which organisms lived, called paleoenvironments, and the pathways leading to their fossilization.

Fossilization is a physical-chemical process that typically requires three conditions 1) possession of hard parts, 2) escape from immediate destruction, and 3) the right geochemical conditions in the sediment. First, organisms with hard parts like wood, bones, teeth, shells, or other mineralized parts, are much more likely to leave a fossil of some kind than those that only have soft parts like jellyfish, worms and slugs. Soft parts, like hair, feathers, skin, internal organs, flowers, etc., are extremely rare in the fossil record of the majority of animal and plant groups. The reason is that destruction of soft tissues by microbial decay or scavenging occurs rapidly after death, and only hard, mineralized structures survive long enough to be buried and preserved. That is the main reason why the fossil record is incomplete because, in comparison with the abundance of soft-bodied organisms present in modern environments, few organisms that consisted of only soft parts are represented in the fossil record. The fossil record is thus biased towards the mineralized parts of those organisms that produce them. Soft tissues do not last as long as hard parts, but even with hard parts, some materials endure longer than others. For instance, teeth last much longer than bones, while shells and cellulose endure longer than chitin (the protein that forms the arthropod&rsquos exoskeleton), although the latter is more labile and fragile than lignin. However, some remarkable examples of preserved soft parts exist, including entire mammoths preserved in Siberian permafrost salamanders, flowers, insects, arachnids, and other invertebrates preserved in amber[1] and blood vessels and cells preserved in dinosaur bones,[2] bacteria in mineral salt,[3] and bacteria in Cretaceous dinosaur skull bones.[4] An exceptional case is the fossilization of muscles, which is very rare and has been documented in extraordinary specimens as the fossil fish of the Santana Formation, in Brazil.[5] These rare fossils are cases of exceptional preservation (Fig, 1). Despite this bias toward the hard parts of organisms, the fossil record is still considered adequate to study the history of life on earth.

Figure 1: Differential preservation of fossil fish. This image illustrates two modes of preservation in fossil fish. The fish on the left (Leptolepsis knorri) shows the common mode of preservation in 2D, with the skeleton, including the skull, and part of the skin (scales) preserved with a fair degree of articulation and completeness. The fish on the right (Araripelepidotes), from the Santana Formation in NE Brazil, is a case of exceptional preservation in which the body is preserved in three dimensions. Studies have shown that some of these three-dimensional fish contain parts of the soft tissue (including muscles, gills, and internal organs) mineralized in hydroxyapatite, preserving even the fine structure of the muscle myomeres and other details. The rapid destruction of dead fish in modern environments suggests that rapid burial and mineralization must have occurred to preserve the carcasses of these fossil fish.

A second important factor is that fossilization requires escape from immediate destruction after death. Modern observations tell us that only a very small proportion of the organisms living in a given environment will eventually become fossilized. As indicated above, soft-bodied animals are subject to destruction by predation, scavenging, or decay, and normally no remains are left after a short period of time. Plants are also destroyed by herbivores or decomposed by bacterial and fungal activity. Wood can last for relatively long periods of time making it more likely to be buried and fossilized. Animals with hard skeletons are also subject to destruction, but their hard parts may remain and become fossilized.

Most organisms do not become fossils. Why is that? The reason is that both organic and mineral matter are destroyed by bacterial decay and physical damage. Soon after the organism dies, bacteria initiate the process of decomposition by breaking down molecules and tissues. Moreover, physical processes, like water currents, trampling or scavenging, can contribute to the destruction of the remains.

But bacteria may also play an important role in the opposite process&mdashpreservation, the mineralization of remains in certain environmental settings. Bacterial activity plays an important part in the chemistry of calcite (CaCO3),[6] which is the main component of calcareous rocks and many fossils. Dolomite (CaMgCO3), siderite (FeCO3), and phosphates are also precipitated by bacterial activity. Bacteria&rsquos extraordinary capacity for multiplication favors the early onset of certain biomineralization processes that prevent destruction of organic remains. Thus, fossilization depends on two chemical parameters: decay, which destroys the remains of organisms, and mineralization, which preserves a record of their existence. Interestingly, decay is carried out by bacterial activity, which also is the cause of many instances of mineralization.

Figure 2: Geocoma is a fossil brittle star found in Jurassic rocks in Europe. These invertebrate animals were very delicate, without an internal skeleton, and would decay and disarticulate rapidly after death in an aquatic environment. The fact that this fossil is preserved in its entirety and in articulation indicates that very little time passed between death, burial, and fossilization. Actually, it is likely that an event of sudden burial killed the animal and started the mineralization processes.

The key to fossil formation is thus rapid burial in a medium capable of preventing or retarding complete decay. The remains of organisms must be buried before decay and scavenging completely destroy them (Fig, 2). The occurrence of fossil bones, shells, and wood indicates that not only were these remains buried before complete destruction occurred, but also that further decay ceased and chemical conditions in the sediment were appropriate for preservation. Therefore, the third condition for fossilization to occur is the existence of the right geochemical conditions in the sediment for remineralization to occur. The type of chemical conditions depends on the environment in which the organisms were buried. Different conditions and environments may yield different types of preservation, variation in abundance, or a complete lack of fossils. Marine animals living in shallow waters are the most likely to be preserved, especially if fine sediments like mud or sand cover them. Terrestrial organisms are not as likely to be preserved as those from marine habitats. The remains of terrestrial faunas and floras are normally encountered in lacustrine, swamp, and fluvial-alluvial deposits because water is almost absolutely necessary for fossilization.

Water flowing in the sediment surrounding buried organisms allows dissolved minerals to seep through bones, shells, wood or other hard parts and replace them with minerals. This process is known as permineralization. Calcium will precipitate into calcite, a form of calcium carbonate, and silicon will precipitate into silica these are the two most abundant minerals or cements that produce mineralization of organic matter. Minerals containing copper, cobalt, or iron may add color to fossils.

Contrary to what many people believe, permineralization may not take a long time. Given the right geochemical conditions during burial, permineralization can occur rapidly: ranging from within a few hours to a few years, depending on the size and nature of the original material. Scientists have reported fossilized embryos of echinoderms (sea urchins), which are extremely delicate structures. Experiments carried out to replicate those fossilized embryos show that fossilization happened in a very short span of time.[7] Experiments show that mineralization of soft tissue of shrimp with calcium phosphate mediated by bacterial decomposition may start in a few days and increase in 4 to 8 weeks after death, possibly leading to fossilization.[8] This is an example of fossilization involving mineral precipitation that occurs during the decay process caused by bacteria. The British paleontologists David Martill studied in detail the preservation of fishes and other animals in rocks of the Lower Cretaceous of the Chapada do Araripe, north-east Brazil, and found that they have preserved the most delicate structures known in the fossil record. Gills, muscles, stomachs and even eggs with yolks have been found. These are cases of exceptional preservation by phosphatization&mdashmineralization by calcium phosphate. Martill concludes that many of the fine details preserved in those fossils became mineralized within a span of time of 5 hours or less after death, and calls this instantaneous fossilization.[9] I have studied fossils of whales in the Pisco Formation in Peru in which the baleen structure (the filtering organ in the mouth of the whales) has been partially mineralized and preserved in anatomical position, which is a case of exceptional preservation because baleen is not bony tissue and is not rooted in the maxillary. Baleen tends to detach from the whale and decay rather quickly after death, nevertheless it is preserved in life position in many of those fossil specimens. I have suggested that the whales must have been rapidly buried and the baleen rapidly mineralized in order to become preserved.[10]

In conclusion, fossilization at least at the present time, is thought to be a very unlikely process and it is believed that only a very small fraction of organisms that lived in the past became fossils. The majority of these fossils were hard skeletal parts or wood. To become fossilized, organisms must be rapidly buried, preferably in a fine sediment with geochemical conditions that favor the exchange of minerals between the sediment and organic components of the organism, and that exchange of minerals is possible because of dissolved minerals in flowing water. If those conditions occur, fossilization must necessarily be a rapid process of a few hours to a few months if it is to occur before decay destroys any record of the organism. Fossilization does not take thousands or millions of years, but is most likely to occur in catastrophic conditions such as would have existed during the Genesis Flood.

Raúl Esperante
Geoscience Research Institute


[1] Poinar, G. Jr., Wake, D. B. 2015. Palaeoplethodon hispaniolaegen. n., sp. n. (Amphibia: Caudata), a fossil salamander from the Caribbean. Palaeodiversity 8:21-29 Poinar, G. O. Jr., Struwe, L. 2016. An asteroid flower from neotropical mid-Tertiary amber. Nature Plants2, article number 16005 Poinar, G. O. Jr., Brwon, A. E. 2016. An exotic insect Aethiocarenus burmanicusgen. et sp. Nov. (Aethiocarenodea ord. nov., Aethiocarenidae fam. Nov.) from mid-Cretaceous Myanmar amber. Cretaceous Research 72:100-104,

[2]Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R., Toporski, J. K. 2005. Soft-tissue vessels and cellular preservation in Tyrannosaurs rex. Science307:1952-1955.

[3] Monastersky, R. 1995. Ancient Bacteria Brought Back to Life. Science News147(20):308.

[4] Pinheiro, F. L. Horn, B. L. D. Schultz, C. L., de Andrade, J. A. F. G., Sucerquia, P. A. 2012. Fossilized bacteria in a Cretaceous pterosaur headcrest. Lethaia45: 495-499.

[5] Martill, D. M. 1989. The Medusa Effect: Instantaneous fossilization. Geology Today(November-December): 201-205.

[6] Anbu, P., Kang, C. H., Shin, Y. J., So, J. S. 2016. Formations of calcium carbonate minerals by bacteria and its multiple applications. SpringerPlus, 5, 250. doi:10.1186/s40064-016-1869-2.

[7] Raff, Elizabeth C., Schollaert, Kaila L., Nelson, David E., Donoghue, Philip C. J., Thomas, Ceri-Wyn, Turner, F. Rudolf Stein, Barry D., Dong, Xiping, Bengtson, Stefan, Huldtgren, Therese, Stampanoni, Marco, Chongyu, Yin, Raff, Rudolf A. 2008. Embryo fossilization is a biological process mediated by microbial biofilms. PNAS105(49):19360-19365, 10.1073/pnas.0810106105.

[8] Briggs, Derek E. G., Kear, Amanda J. 1993. Fossilization of Soft Tissue in the Laboratory. Science259(5100): 1439-1442. DOI: 10.1126/science.259.5100.1439.

[10] Esperante, R., Brand, L. R., Nick, Kevin E., Poma, O., Urbina, M. 2008. Exceptional occurrence of fossil baleen in shallow marine sediments of the Neogene Pisco Formation, Southern Peru. Palaeogeography, Palaeoclimatology, Palaeoecology257(3):344-360.

Watch the video: Ιοί - Βακτήρια Αρχές Νοσολογίας απλουστευμένες - PART 1 (June 2022).