A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. They colonize environments ranging in temperature from –40 °C to 120 °C. A few are found as endosymbionts of animals.
Although only a few centimetres thick at most, microbial mats create a wide range of internal chemical environments, and hence generally consist of layers of microorganisms that can feed on or at least tolerate the dominant chemicals at their level and which are usually of closely related species. In moist conditions mats are usually held together by slimy substances secreted by the microorganisms, and in many cases some of the microorganisms form tangled webs of filaments which make the mat tougher. The best known physical forms are flat mats and stubby pillars called stromatolites, but there are also spherical forms.
Microbial mats are the earliest form of life on Earth for which there is good fossil evidence, from , and have been the most important members and maintainers of the planet's ecosystems. Originally they depended on hydrothermal vents for energy and chemical "food", but the development of photosynthesis allow mats to proliferate outside of these environments by utilizing a more widely available energy source, sunlight. The final and most significant stage of this liberation was the development of oxygen-producing photosynthesis, since the main chemical inputs for this are carbon dioxide and water.
As a result, microbial mats began to produce the atmosphere we know today, in which free oxygen is a vital component. At around the same time they may also have been the birthplace of the more complex eukaryote type of cell, of which all multicellular organisms are composed. Microbial mats were abundant on the shallow seabed until the Cambrian substrate revolution, when animals living in shallow seas increased their burrowing capabilities and thus broke up the surfaces of mats and let oxygenated water into the deeper layers, poisoning the oxygen-intolerant microorganisms that lived there. Although this revolution drove mats off soft floors of shallow seas, they still flourish in many environments where burrowing is limited or impossible, including rocky seabeds and shores, hyper-saline and brackish lagoons, and are found on the floors of the deep oceans.
Because of microbial mats' ability to use almost anything as "food", there is considerable interest in industrial uses of mats, especially for water treatment and for cleaning up pollution.
Microbial mats have also been referred to as "algal mats" and "bacterial mats" in older scientific literature. They are a type of biofilm that is large enough to see with the naked eye and robust enough to survive moderate physical stresses. These colonies of bacteria form on surfaces at many types of interface, for example between water and the sediment or rock at the bottom, between air and rock or sediment, between soil and bed-rock, etc. Such interfaces form vertical chemical gradients, i.e. vertical variations in chemical composition, which make different levels suitable for different types of bacteria and thus divide microbial mats into layers, which may be sharply defined or may merge more gradually into each other. A variety of microbes are able to transcend the limits of diffusion by using "nanowires" to shuttle electrons from their metabolic reactions up to two centimetres deep in the sediment – for example, electrons can be transferred from reactions involving hydrogen sulfide deeper within the sediment to oxygen in the water, which acts as an electron acceptor.
The best-known types of microbial mat may be flat laminated mats, which form on approximately horizontal surfaces, and stromatolites, stubby pillars built as the microbes slowly move upwards to avoid being smothered by sediment deposited on them by water. However, there are also spherical mats, some on the outside of pellets of rock or other firm material and others inside spheres of sediment.
A microbial mat consists of several layers, each of which is dominated by specific types of microorganism, mainly bacteria. Although the composition of individual mats varies depending on the environment, as a general rule the by-products of each group of microorganisms serve as "food" for other groups. In effect each mat forms its own food chain, with one or a few groups at the top of the food chain as their by-products are not consumed by other groups. Different types of microorganism dominate different layers based on their comparative advantage for living in that layer. In other words, they live in positions where they can out-perform other groups rather than where they would absolutely be most comfortable — ecological relationships between different groups are a combination of competition and co-operation. Since the metabolic capabilities of bacteria (what they can "eat" and what conditions they can tolerate) generally depend on their phylogeny (i.e. the most closely related groups have the most similar metabolisms), the different layers of a mat are divided both by their different metabolic contributions to the community and by their phylogenetic relationships.
In a wet environment where sunlight is the main source of energy, the uppermost layers are generally dominated by aerobic photosynthesizing cyanobacteria (blue-green bacteria whose color is caused by their having chlorophyll), while the lowest layers are generally dominated by anaerobic sulfate-reducing bacteria. Sometimes there are intermediate (oxygenated only in the daytime) layers inhabited by facultative anaerobic bacteria. For example, in hypersaline ponds near Guerrero Negro (Mexico) various kind of mats were explored. There are some mats with a middle purple layer inhabited by photosynthesizing purple bacteria. Some other mats have a white layer inhabited by chemotrophic sulfide-oxidizing bacteria and beneath them an olive layer inhabited by photosynthesizing green sulfur bacteria and heterotrophic bacteria. However, this layer structure is not changeless during a day: some species of cyanobacteria migrate to deeper layers at morning, and go back at evening, to avoid intensive solar light and UV radiation at mid-day.
Microbial mats are generally held together and bound to their substrates by slimy extracellular polymeric substances which they secrete. In many cases some of the bacteria form filaments (threads), which tangle and thus increase the colonies' structural strength, especially if the filaments have sheaths (tough outer coverings).
This combination of slime and tangled threads attracts other microorganisms which become part of the mat community, for example protozoa, some of which feed on the mat-forming bacteria, and diatoms, which often seal the surfaces of submerged microbial mats with thin, parchment-like coverings.
Marine mats may grow to a few centimeters in thickness, of which only the top few millimeters are oxygenated.
Underwater microbial mats have been described as layers that live by exploiting and to some extent modifying local chemical gradients, i.e. variations in the chemical composition. Thinner, less complex biofilms live in many sub-aerial environments, for example on rocks, on mineral particles such as sand, and within soil. They have to survive for long periods without liquid water, often in a dormant state. Microbial mats that live in tidal zones, such as those found in the Sippewissett salt marsh, often contain a large proportion of similar microorganisms that can survive for several hours without water.
Microbial mats and less complex types of biofilm are found at temperature ranges from –40 °C to +120 °C, because variations in pressure affect the temperatures at which water remains liquid.
Microbial mats use all of the types of metabolism and feeding strategy that have evolved on Earth—anoxygenic and oxygenic photosynthesis; anaerobic and aerobic chemotrophy (using chemicals rather than sunshine as a source of energy); organic and inorganic respiration and fermentation (i..e converting food into energy with and without using oxygen in the process); autotrophy (producing food from inorganic compounds) and heterotrophy (producing food only from organic compounds, by some combination of predation and detritivory).
Most sedimentary rocks and ore deposits have grown by a reef-like build-up rather than by "falling" out of the water, and this build-up has been at least influenced and perhaps sometimes caused by the actions of microbes. Stromatolites, bioherms (domes or columns similar internally to stromatolites) and biostromes (distinct sheets of sediment) are among such microbe-influenced build-ups. Other types of microbial mat have created wrinkled "elephant skin" textures in marine sediments, although it was many years before these textures were recognized as trace fossils of mats. Microbial mats have increased the concentration of metal in many ore deposits, and without this it would not be feasible to mine them—examples include iron (both sulfide and oxide ores), uranium, copper, silver and gold deposits.
Microbial mats are among the oldest clear signs of life, as microbially induced sedimentary structures (MISS) formed have been found in western Australia. At that early stage the mats' structure may already have been similar to that of modern mats that do not include photosynthesizing bacteria. It is even possible that non-photosynthesizing mats were present as early as . If so, their energy source would have been hydrothermal vents (high-pressure hot springs around submerged volcanoes), and the evolutionary split between bacteria and archea may also have occurred around this time.
The earliest mats were probably small, single-species biofilms of chemotrophs that relied on hydrothermal vents to supply both energy and chemical "food". Within a short time (by geological standards) the build-up of dead microorganisms would have created an ecological niche for scavenging heterotrophs, possibly methane-emitting and sulfate-reducing organisms that would have formed new layers in the mats and enriched their supply of biologically useful chemicals.
It is generally thought that photosynthesis, the biological generation of energy from light, evolved shortly after (3 billion). However an isotope analysis suggests that oxygenic photosynthesis may have been widespread as early as . The eminent researcher into Earth's earliest life, William Schopf, argues that, if one did not know their age, one would classify some of the fossil organisms in Australian stromatolites from as cyanobacteria, which are oxygen-producing photosynthesizers. There are several different types of photosynthetic reaction, and analysis of bacterial DNA indicates that photosynthesis first arose in anoxygenic purple bacteria, while the oxygenic photosynthesis seen in cyanobacteria and much later in plants was the last to evolve.
The earliest photosynthesis may have been powered by infra-red light, using modified versions of pigments whose original function was to detect infra-red heat emissions from hydrothermal vents. The development of photosynthetic energy generation enabled the microorganisms first to colonize wider areas around vents and then to use sunlight as an energy source. The role of the hydrothermal vents was now limited to supplying reduced metals into the oceans as a whole rather than being the main supporters of life in specific locations. Heterotrophic scavengers would have accompanied the photosynthesizers in their migration out of the "hydrothermal ghetto".
The evolution of purple bacteria, which do not produce or use oxygen but can tolerate it, enabled mats to colonize areas that locally had relatively high concentrations of oxygen, which is toxic to organisms that are not adapted to it. Microbial mats would have been separated into oxidized and reduced layers, and this specialization would have increased their productivity. It may be possible to confirm this model by analyzing the isotope ratios of both carbon and sulfur in sediments laid down in shallow water.
The last major stage in the evolution of microbial mats was the appearance of cyanobacteria, photosynthesizers which both produce and use oxygen. This gave undersea mats their typical modern structure: an oxygen-rich top layer of cyanobacteria; a layer of photosynthesizing purple bacteria that could tolerate oxygen; and oxygen-free, H2S-dominated lower layers of heterotrophic scavengers, mainly methane-emitting and sulfate-reducing organisms.
It is estimated that the appearance of oxygenic photosynthesis increased biological productivity by a factor of between 100 and 1,000. All photosynthetic reactions require a reducing agent, but the significance of oxygenic photosynthesis is that it uses water as a reducing agent, and water is much more plentiful than the geologically produced reducing agents on which photosynthesis previously depended. The resulting increases in the populations of photosynthesizing bacteria in the top layers of microbial mats would have caused corresponding population increases among the chemotrophic and heterotrophic microorganisms that inhabited the lower layers and which fed respectively on the by-products of the photosynthesizers and on the corpses and / or living bodies of the other mat organisms. These increases would have made microbial mats the planet's dominant ecosystems. From this point onwards life itself produced significantly more of the resources it needed than did geochemical processes.
Oxygenic photosynthesis in microbial mats would also have increased the free oxygen content of the Earth's atmosphere, both directly by emitting oxygen and because the mats emitted molecular hydrogen (H2), some of which would have escaped from the Earth's atmosphere before it could re-combine with free oxygen to form more water. Microbial mats thus played a major role in the evolution of organisms which could first tolerate free oxygen and then use it as an energy source. Oxygen is toxic to organisms that are not adapted to it, but greatly increases the metabolic efficiency of oxygen-adapted organisms — for example anaerobic fermentation produces a net yield of two molecules of adenosine triphosphate, cells' internal "fuel", per molecule of glucose, while aerobic respiration produces a net yield of 36. The oxygenation of the atmosphere was a prerequisite for the evolution of the more complex eukaryote type of cell, from which all multicellular organisms are built.
Cyanobacteria have the most complete biochemical "toolkits" of all the mat-forming organisms: the photosynthesis mechanisms of both green bacteria and purple bacteria; oxygen production; and the Calvin cycle, which converts carbon dioxide and water into carbohydrates and sugars. It is likely that they acquired many of these sub-systems from existing mat organisms, by some combination of horizontal gene transfer and endosymbiosis followed by fusion. Whatever the causes, cyanobacteria 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, which forms the basis of most marine food chains.
The time at which eukaryotes first appeared is still uncertain: there is reasonable evidence that fossils dated between and represent eukaryotes, but the presence of steranes in Australian shales may indicate that eukaryotes were present . There is still debate about the origins of eukaryotes, and many of the theories focus on the idea that a bacterium first became an endosymbiont of an anaerobic archean and then fused with it to become one organism. If such endosymbiosis was an important factor, microbial mats would have encouraged it. There are two possible variations of this scenario:
Microbial mats from ~provide the first evidence of life in the terrestrial realm.
The Ediacara biota are the earliest widely accepted evidence of multicellular "animals". Most Ediacaran strata with the "elephant skin" texture characteristic of microbial mats contain fossils, and Ediacaran fossils are hardly ever found in beds that do not contain these microbial mats. Adolf Seilacher categorized the "animals" as: "mat encrusters", which were permanently attached to the mat; "mat scratchers", which grazed the surface of the mat without destroying it; "mat stickers", suspension feeders that were partially embedded in the mat; and "undermat miners", which burrowed underneath the mat and fed on decomposing mat material.
In the Early Cambrian, however, organisms began to burrow vertically for protection or food, breaking down the microbial mats, and thus allowing water and oxygen to penetrate a considerable distance below the surface and kill the oxygen-intolerant microorganisms in the lower layers. As a result of this Cambrian substrate revolution, marine microbial mats are confined to environments in which burrowing is non-existent or negligible: very harsh environments, such as hyper-saline lagoons or brackish estuaries, which are uninhabitable for the burrowing organisms that broke up the mats; rocky "floors" which the burrowers cannot penetrate; the depths of the oceans, where burrowing activity today is at a similar level to that in the shallow coastal seas before the revolution.
Although the Cambrian substrate revolution opened up new niches for animals, it was not catastrophic for microbial mats, but it did greatly reduce their extent.
Most fossils preserve only the hard parts of organisms, e.g. shells. The rare cases where soft-bodied fossils are preserved (the remains of soft-bodied organisms and also of the soft parts of organisms for which only hard parts such as shells are usually found) are extremely valuable because they provide information about organisms that are hardly ever fossilized and much more information than is usually available about those for which only the hard parts are usually preserved. Microbial mats help to preserve soft-bodied fossils by:
The ability of microbial mat communities to use a vast range of "foods" has recently led to interest in industrial uses. There have been trials of microbial mats for purifying water, both for human use and in fish farming, and studies of their potential for cleaning up oil spills. As a result of the growing commercial potential, there have been applications for and grants of patents relating to the growing, installation and use of microbial mats, mainly for cleaning up pollutants and waste products.
Afifella pfennigii is a bacterial species from the genus Afifella which has been isolated from benthic microbial mat from a brackish water pond on the Rangiroa Atoll on the French Polynesia Islands.Algal mat
Algal mats are one of many types of microbial mat that forms on the surface of water or rocks. They are typically composed of blue-green cyanobacteria and sediments. Formation occurs when alternating layers of blue-green bacteria and sediments are deposited or grow in place, creating dark-laminated layers. Stromatolites are prime examples of algal mats. Algal mats played an important role in the Great Oxidation Event on Earth some 2.3 billion years ago. Algal mats can become a significant ecological problem, if the mats grow so expansive or thick as to disrupt the other underwater marine life by blocking the sunlight or producing toxic chemicals.Cambrian substrate revolution
The "Cambrian substrate revolution" or "Agronomic revolution", evidenced in trace fossils, is the diversification of animal burrowing during the early Cambrian period.
Before this "widening of the behavioural repertoire", bottom-dwelling animals mainly grazed on the microbial mats that lined the surface, crawling above or burrowing just below them. These microbial mats created a barrier between the water and the sediment underneath, which was less water-logged than modern sea-floors, and almost completely anoxic (lacking in oxygen). As a result, the substrate was inhabited by sulfate-reducing bacteria, whose emissions of hydrogen sulfide (H2S) made the substrate toxic to most other organisms.Around the start of the Cambrian, organisms began to burrow vertically, forming a great diversity of different fossilisable burrow forms as they penetrated the sediment for protection or to feed.
These burrowing animals broke down the microbial mats, and thus allowed water and oxygen to penetrate a considerable distance below the surface. This restricted the sulfate-reducing bacteria and their H2S emissions to the deeper layers, making the upper layers of the sea-floor habitable for a much wider range of organisms. The upper level of the sea-floor became wetter and softer as it was constantly churned up by burrowers.Clostridium lacusfryxellense
Clostridium lacusfryxellense is a psychrophilic, Gram-positive, spore-forming and anaerobic bacterium from the genus of Clostridium which has been isolated from a microbial mat from Lake Fryxell in Antarctica.Common descent
Common descent describes how, in evolutionary biology, a group of organisms share a most recent common ancestor. There is massive evidence of common descent of all life on Earth from the last universal common ancestor (LUCA). In July 2016, scientists reported identifying a set of 355 genes from the LUCA by comparing the genomes of the three domains of life, archaea, bacteria, and eukaryotes.Common ancestry between organisms of different species arises during speciation, in which new species are established from a single ancestral population. Organisms which share a more-recent common ancestor are more closely related. The most recent common ancestor of all currently living organisms is the last universal ancestor, which lived about 3.9 billion years ago. The two earliest evidences for life on Earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. All currently living organisms on Earth share a common genetic heritage, though the suggestion of substantial horizontal gene transfer during early evolution has led to questions about the monophyly (single ancestry) of life. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian.Universal common descent through an evolutionary process was first proposed by the British naturalist Charles Darwin in the concluding sentence of his 1859 book On the Origin of Species:
There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.Fictibacillus halophilus
Fictibacillus halophilus is a moderately halophilic, Gram-positive, spore-forming and motile bacterium from the genus of Fictibacillus which has been isolated from microbial mat from a hot spring in Manikaran in India.Flavobacterium degerlachei
Flavobacterium degerlachei is a Gram-negative, rod-shaped and psychrophilic bacterium from the genus of Flavobacterium which has been isolated from microbial mat from the Lake Ace in the Antarctica.Halorhodospira neutriphila
Halorhodospira neutriphila is a bacterium from the genus of Halorhodospira which has been isolated from a microbial mat from a marine saltern from Rhone Delta in France.Hot Lake (Washington)
Hot Lake is a hypersaline, meromictic lake located in extreme northern Okanogan County, Washington near Oroville, Washington. Occupying a small, glacially-carved basin surrounded by mafic magnesian rocks, dolomites, and shales containing deposits of pyrite and pyrrholite minerals, Hot Lake is unusual among hypersaline lakes in that it is dominated by magnesium and sulfate as its major ions. Because of its mineralogy, Hot Lake was mined for epsomite, initially by the Stewart-Calvert Company during World War I, when the importation of epsomite from Germany was suspended. Major flora growing within the lake include Ruppia maritima and Chara, and the dominant fauna are the brine shrimp Artemia salina and Branchinecta campestris. A benthic phototrophic microbial mat dominated by cyanobacteria is also found within the lake.Mariprofundus ferrooxydans
Mariprofundus ferrooxydans is a neutrophilic, chemolithotrophic, Gram-negative bacterium which can grow by oxidising ferrous to ferric iron. It is the sole member of the class Zetaproteobacteria in the phylum Proteobacteria.Microbially induced sedimentary structure
Microbially induced sedimentary structures (MISS) are primary sedimentary structures formed by the interaction of microbes with sediment and physical agents of erosion, deposition, and transportation. The structures commonly form when microbial mats (which may comprise bacteria, fungi, protozoans, archaea or algae) are preserved in the sedimentary geological record. There are 17 main types of macroscopic and microscopic MISS. Of those, wrinkle structures and microbial mat chips are the most abundant in the fossil record. Other MISS include sinoidal structures, polygonal oscillation cracks, multidirected ripple marks, erosional remnants and pockets, or gas domes.
Although these structures have only recently been named and systematically described, links between microbes and distinctive structures in sediments and sedimentary rocks have been suggested by several early workers. MISS have been identified in beds formed 3,480 million years ago in the Archean and may be the oldest complete fossils on Earth. In the Ediacaran period, they are often associated with the preservation of fossils of the Ediacara biota; subsequent to this point their prevalence declines as a result of the Agronomic revolutionA number of criteria have been proposed for recognising genuinely biological structures, and discriminating them from similar-looking features that can arise through geological processes. These relate to the extent of metamorphism to which the rocks have been subjected; their stratigraphic position with respect to sea-level; their depositional environment; their relationship to ancient hydraulics; and their texture.Individual studies on microbial mat-induced sedimentary structures are summarized and illustrated in several recent books, including Atlas of microbial mat features preserved in the siliciclastic rock record and Microbial Mats in Siliciclastic Depositional Systems Through Time.According to a study on the planet Mars, there may be sandstone beds, associated with the Gillespie Lake Member of Yellowknife Bay, visited by the Curiosity rover, that are similar to MISS on Earth.Ornatilinea
Ornatilinea is a bacteria genus from the family of Anaerolineaceae with one known species (Ornatilinea apprima). Ornatilinea apprima has been isolated from microbial mat from a anaerobic sludge blanket reactor from the Tomsk Region in Russia.Reef
A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water.
Many reefs result from natural, abiotic processes—deposition of sand, wave erosion planing down rock outcrops, etc.—but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.
Artificial reefs (e.g. shipwrecks) sometimes have a role in enhancing the physical complexity of featureless sand bottoms, in order to attract a diverse assemblage of organisms, especially algae and fish.
Earth's largest reef system is the Great Barrier Reef in Australia, at a length of over 2,300 kilometres (1,400 miles).Rhodoferax antarcticus
Rhodoferax antarcticus is a psychrophilic, phototrophic, nonsulfur, highly motile bacterium from the genus Rhodoferax, which was isolated from an Antarctic microbial mat in Ross Island.Sippewissett Microbial Mat
The Sippewissett Salt Marsh/ Microbial Mat is located along the lower eastern Buzzards Bay shoreline of Cape Cod, about 5 miles north of Woods Hole and 1 mile southwest of West Falmouth, Massachusetts, in the United States. The marsh has two regions, the Great Sippewisset Marsh to the north and Little Sippewisset Marsh to the south, separated from each other by a narrow tongue of land (Saconesset Hills). The marsh extends into an estuary in which the intertidal zone provides a dynamic environment that supports a diverse ecology, including threatened and endangered species such as the roseate tern (Sterna dougallii). The ecology of the salt marsh is based in and supported by the microbial mats which cover the ground of the marsh.Snottite
Snottite, also snoticle, is a microbial mat of single-celled extremophilic bacteria which hang from the walls and ceilings of caves and are similar to small stalactites, but have the consistency of nasal mucus. In the Frasassi Caves in Italy, over 70% of cells in Snottite have been identified as Acidithiobacillus thiooxidans, with smaller populations including an archaeon in the uncultivated 'G-plasma' clade of Thermoplasmatales (>15%) and a bacterium in the Acidimicrobiaceae family (>5%).The bacteria derive their energy from chemosynthesis of volcanic sulfur compounds including H2S and warm-water solution dripping down from above, producing sulfuric acid. Because of this, their waste products are highly acidic (approaching pH=0), with similar properties to battery acid. Researchers at the University of Texas have suggested that this sulfuric acid may be a more significant cause of cave formation than the usual explanation offered of the carbonic acid formed from carbon dioxide dissolved in water.Snottites were brought to attention by researchers Diana Northup and Penny Boston studying them (and other organisms) in a toxic sulfur cave called Cueva de Villa Luz (Cave of the Lighted House), in Tabasco, Mexico. The term "snottite" was given to these cave features by Jim Pisarowicz in 1986.
Brian Cox's BBC series Wonders of the Solar System saw a scientist examining snottites in the caves and positing that if there is life on Mars, it may be similarly primitive and hidden beneath the surface of the Red Planet.Tepidibacillus infernus
Tepidibacillus infernus is an aerotolerant anaerobic, organotrophic, spore-forming and moderately thermophilic bacterium from the genus of Tepidibacillus which has been isolated from microbial mat from the TauTona Gold Mine in South Africa.Thiorhodococcus mannitoliphagus
Thiorhodococcus mannitoliphagus is a bacterium from the genus of Thiorhodococcus which has been isolated from a microbial mat from the White Sea.Zetaproteobacteria
The class Zetaproteobacteria is the sixth and most recently described class of the Proteobacteria. Zetaproteobacteria can also refer to the group of organisms assigned to this class. The Zetaproteobacteria are represented by a single described species, Mariprofundus ferrooxydans, which is an iron-oxidizing neutrophilic chemolithoautotroph originally isolated from Loihi Seamount in 1996 (post-eruption). Molecular cloning techniques focusing on the small subunit ribosomal RNA gene have also been used to identify a more diverse majority of the Zetaproteobacteria that have as yet been unculturable.Regardless of culturing status, the Zetaproteobacteria show up worldwide in estuarine and marine habitats associated with opposing steep redox gradients of reduced (ferrous) iron and oxygen, either as a minor detectable component or as the dominant member of the microbial community. Zetaproteobacteria have been most commonly found at deep-sea hydrothermal vents, though recent discovery of members of this class in near-shore environments has led to the reevaluation of Zetaproteobacteria distribution and significance.