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Marine prokaryotes are marine bacteria and marine archaea. They are defined by their habitat as that live in Marine habitat, that is, in the saline water of seas or oceans or the brackish water of coastal Estuary. All cellular can be divided into prokaryotes and eukaryotes. are whose cells have a cell nucleus enclosed within membranes, whereas prokaryotes are the organisms that do not have a nucleus enclosed within a membrane. (2026). 9780007221349, HarperCollins. ISBN 9780007221349 (1983). 9780333348673, Macmillan Press. ISBN 9780333348673 The three-domain system of classifying life adds another division: the prokaryotes are divided into two domains of life, the microscopic bacteria and the microscopic archaea, while everything else, the eukaryotes, become the third domain.
Prokaryotes play important roles in as recycling nutrients. Some prokaryotes are , causing disease and even death in plants and animals. Marine prokaryotes are responsible for significant levels of the photosynthesis that occurs in the ocean, as well as significant cycling of carbon and other nutrients.
Prokaryotes live throughout the biosphere. In 2018 it was estimated the total biomass of all prokaryotes on the planet was equivalent to 77 billion of carbon (77 Gigatonne C). This is made up of 7 Gt C for archaea and 70 Gt C for bacteria. These figures can be contrasted with the estimate for the total biomass for animals on the planet, which is about 2 Gt C, and the total biomass of humans, which is 0.06 Gt C. This means archaea collectively have over 100 times the collective biomass of humans, and bacteria over 1000 times.
There is no clear evidence of life on Earth during the first 600 million years of its existence. When life did arrive, it was dominated for 3,200 million years by the marine prokaryotes. More complex life, in the form of crown eukaryotes, did not appear until the Cambrian explosion a mere 500 million years ago.
Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry.
Prokaryotes inhabited the Earth from approximately 3–4 billion years ago.
No obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years. The eukaryotic cells emerged between 1.6 and 2.7 billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called endosymbiont. The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or . Another engulfment of -like organisms led to the formation of chloroplasts in algae and plants.
The history of life was that of the unicellular prokaryotes and eukaryotes until about 610 million years ago when multicellular organisms began to appear in the oceans in the Ediacara biota period. The evolution of multicellularity occurred in multiple independent events, in organisms as diverse as , brown algae, cyanobacteria, and myxobacteria. In 2016 scientists reported that, about 800 million years ago, a minor genetic change in a single molecule called GK-PID may have allowed organisms to go from a single cell organism to one of many cells.
Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over a span of about 10 million years, in an event called the Cambrian explosion. Here, the majority of Phylum of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.
The division of life forms between prokaryotes and eukaryotes was firmly established by the microbiologists Roger Stanier and C. B. van Niel in their 1962 paper, The concept of a bacterium. One reason for this classification was so what was then often called blue-green algae (now called cyanobacteria) would cease to be classified as plants but grouped with bacteria.
In 1990 Carl Woese et al. introduced the three-domain system. The prokaryotes were split into two domains, the archaea and the bacteria, while the eukaryotes become a domain in their own right. The key difference from earlier classifications is the splitting of archaea from bacteria.
The earliest evidence for life on earth comes from biogenic carbon signatures and stromatolite fossils discovered in 3.7 billion-year-old rocks. In 2015, possible "remains of Biotic material" were found in 4.1 billion-year-old rocks. In 2017 putative evidence of possibly the oldest forms of life on Earth was reported in the form of fossilized discovered in hydrothermal vent precipitates that may have lived as early as 4.28 billion years ago, not long after the oceans formed 4.4 billion years ago, and not long after the formation of the Earth 4.54 billion years ago.
Microbial mats of coexisting bacteria and archaea were the dominant form of life in the early Archean Eon and many of the major steps in early evolution are thought to have taken place in this environment. The evolution of photosynthesis around 3.5 Ga resulted in a buildup of its waste product oxygen in the atmosphere, leading to the great oxygenation event beginning around 2.4 Ga.
The earliest evidence of eukaryotes dates from 1.85 Ga, and while they may have been present earlier, their diversification accelerated when they started using oxygen in their metabolism. Later, around 1.7 Ga, multicellular organisms began to appear, with differentiated cells performing specialised functions.
A stream of airborne microorganisms, including prokaryotes, circles the planet above weather systems but below commercial air lanes. Some peripatetic microorganisms are swept up from terrestrial dust storms, but most originate from marine microorganisms in sea spray. In 2018, scientists reported that hundreds of millions of viruses and tens of millions of bacteria are deposited daily on every square meter around the planet.
Microscopic life undersea is diverse and still poorly understood, such as for the role of in marine ecosystems. Most marine viruses are , which are harmless to plants and animals, but are essential to the regulation of saltwater and freshwater ecosystems. (2026). 9781284025927, Jones and Bartlett Publishers. ISBN 9781284025927 They infect and destroy bacteria and archaea in aquatic microbial communities, and are the most important mechanism of carbon cycle in the marine environment. The organic molecules released from the dead bacterial cells stimulate fresh bacterial and algal growth. Viral activity may also contribute to the biological pump, the process whereby carbon is sequestered in the deep ocean.
Once regarded as constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other , bacterial cells do not contain a cell nucleus and rarely harbour cell membrane . Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two very different groups of organisms that evolution from an ancient common ancestor. These evolutionary domains are called Bacteria and Archaea.
The ancestors of modern bacteria were unicellular microorganisms that were the Abiogenesis to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. Although bacterial exist, such as , their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species. However, gene sequences can be used to reconstruct the bacterial phylogenetics, and these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiont associations with the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea. This involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondrion or , which are still found in all known Eukarya. Later on, some eukaryotes that already contained mitochondria also engulfed cyanobacterial-like organisms. This led to the formation of in algae and plants. There are also some algae that originated from even later endosymbiotic events. Here, eukaryotes engulfed a eukaryotic algae that developed into a "second-generation" plastid. This is known as secondary endosymbiosis.
Bacteria grow to a fixed size and then reproduce through binary fission, a form of asexual reproduction. Under optimal conditions, bacteria can grow and divide extremely rapidly, and bacterial populations can double as quickly as every 9.8 minutes.
Pelagibacter ubique and its relatives may be the most abundant microorganisms in the ocean, and it has been claimed that they are possibly the most abundant bacteria in the world. They make up about 25% of all microbial plankton cells, and in the summer they may account for approximately half the cells present in temperate ocean surface water. The total abundance of P. ubique and relatives is estimated to be about 2 × 1028 microbes."Candidatus Pelagibacter Ubique." European Bioinformatics Institute. European Bioinformatics Institute, 2011. Web. 08 Jan. 2012. http://www.ebi.ac.uk/2can/genomes/bacteria/Candidatus_Pelagibacter_ubique.html However, it was reported in Nature in February 2013 that the bacteriophage HTVC010P, which attacks P. ubique, has been discovered and is probably the most common organism on the planet.
Roseobacter is also one of the most abundant and versatile microorganisms in the ocean. They are diversified across different types of marine habitats, from coastal to open oceans and from sea ice to sea floor, and make up about 25% of coastal marine bacteria. Members of the Roseobacter genus play important roles in marine biogeochemical cycles and climate change, processing a significant portion of the total carbon in the marine environment. They form symbiotic relationships which allow them to degrade aromatic compounds and uptake trace metals. They are widely used in aquaculture and quorum sensing. During algal blooms, 20–30% of the prokaryotic community are Roseobacter. (2026). 9783319479330, Springer, Cham. ISBN 9783319479330
The largest known bacterium, the marine Thiomargarita namibiensis, can be visible to the naked eye and sometimes attains .
The first primary producers that used photosynthesis were oceanic cyanobacteria about 2.3 billion years ago. The release of molecular oxygen by cyanobacteria as a by-product of photosynthesis induced global changes in the Earth's environment. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of oxygen-intolerant organisms, a dramatic change which redirected the evolution of the major animal and plant species.
The tiny (0.6 μm) marine cyanobacterium Prochlorococcus, discovered in 1986, forms today an important part of the base of the ocean food chain and accounts for much of the photosynthesis of the open ocean and an estimated 20% of the oxygen in the Earth's atmosphere. It is possibly the most plentiful genus on Earth: a single millilitre of surface seawater may contain 100,000 cells or more.
Originally, biologists classified cyanobacteria as an algae, and referred to it as "blue-green algae". The more recent view is that cyanobacteria are bacteria, and hence are not even in the same Kingdom as algae. Most authorities exclude all prokaryotes, and hence cyanobacteria from the definition of algae. (2026). 9780805344165, Pearson Education, Inc. ISBN 9780805344165
Archaea were initially classified as bacteria, but this classification is outdated. Archaeal cells have unique properties separating them from the other two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phylum. Classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their in samples from their environment.
Bacteria and archaea are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat and square-shaped cells of Haloquadratum. Despite this morphological similarity to bacteria, archaea possess and several metabolic pathways that are more closely related to those of eukaryotes, notably the involved in transcription and translation. Other aspects of archaeal biochemistry are unique, such as their reliance on in their , such as . Archaea use more energy sources than eukaryotes: these range from organic compounds, such as sugars, to ammonia, ion or even hydrogen. Salt-tolerant archaea (the Haloarchaea) use sunlight as an energy source, and other species of archaea carbon fixation; however, unlike plants and cyanobacteria, no known species of archaea does both. Archaea reproduce asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no known species forms .
Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle. Thermoproteota (also called Crenarchaeota or eocytes) are a phylum of archaea thought to be very abundant in marine environments and one of the main contributors to the fixation of carbon. (2026). 9780131443297, Prentice Hall. ISBN 9780131443297
Nanoarchaeum equitans is a species of marine archaea discovered in 2002 in a hydrothermal vent. It is a thermophile that grows in temperatures at about . Nanoarchaeum appears to be an obligate symbiont on the archaea Ignicoccus. It must stay in contact with the host organism to survive since Nanoarchaeum equitans cannot synthesize lipids but obtains them from its host. Its cells are only 400 nanometre in diameter, making it one of the smallest known cellular organisms, and the smallest known archaeon.
Marine archaea have been classified as follows:See especially Fig. 4 in
| + Nutritional types in bacterial metabolism | |||
| Sunlight | Organic compounds (photoheterotrophs) or carbon fixation (photoautotrophs) | "Cyanobacteria", Green sulfur bacteria, Chloroflexota, or Purple bacteria | |
| Inorganic compounds | Organic compounds (lithoheterotrophs) or carbon fixation (lithoautotrophs) | Thermodesulfobacteriota, Hydrogenophilaceae, or Nitrospirota | |
| Organic compounds | Organic compounds (chemoheterotrophs) or carbon fixation (chemoautotrophs) | Bacillus, Clostridium or Enterobacteriaceae |
Marine prokaryotes have diversified greatly throughout their long existence. The metabolism of prokaryotes is far more varied than that of eukaryotes, leading to many highly distinct prokaryotic types. For example, in addition to using photosynthesis or for energy, as eukaryotes do, marine prokaryotes may obtain energy from inorganic compounds such as hydrogen sulfide. This enables marine prokaryotes to thrive as in harsh environments as cold as the ice surface of Antarctica, studied in cryobiology, as hot as undersea hydrothermal vents, or in high saline conditions as (). Some marine prokaryotes live in or on the bodies of other marine organisms.
The rotary motor model used by bacteria uses the protons of an electrochemical gradient in order to move their flagella. Torque in the flagella of bacteria is created by particles that conduct protons around the base of the flagellum. The direction of rotation of the flagella in bacteria comes from the occupancy of the proton channels along the perimeter of the flagellar motor.
Some eukaryotic cells also use flagella—and they can be found in some protists and plants as well as animal cells. Eukaryotic flagella are complex cellular projections that lash back and forth, rather than in a circular motion. Prokaryotic flagella use a rotary motor, and the eukaryotic flagella use a complex sliding filament system. Eukaryotic flagella are ATP-driven, while prokaryotic flagella can be ATP-driven (archaea) or Proton pump (bacteria).
Marine environments are generally characterized by low concentrations of nutrients kept in steady or intermittent motion by currents and turbulence. Marine bacteria have developed strategies, such as swimming and using directional sensing–response systems, to migrate towards favorable places in the nutrient gradients. Magnetotactic bacteria utilize Earth's magnetic field to facilitate downward swimming into the oxic–anoxic interface, which is the most favorable place for their persistence and proliferation, in chemically stratified sediments or water columns. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Depending on their latitude and whether the bacteria are north or south of the equator, the Earth's magnetic field has one of the two possible polarities, and a direction that points with varying angles into the ocean depths, and away from the generally more oxygen rich surface. Aerotaxis is the response by which bacteria migrate to an optimal oxygen concentration in an oxygen gradient. Various experiments have clearly shown that magnetotaxis and aerotaxis work in conjunction in magnetotactic bacteria. It has been shown that, in water droplets, one-way swimming magnetotactic bacteria can reverse their swimming direction and swim backwards under reducing conditions (less than optimal oxygen concentration), as opposed to oxic conditions (greater than optimal oxygen concentration).
Regardless of their morphology, all magnetotactic bacteria studied so far are motile by means of flagella. Marine magnetotactic bacteria in particular tend to possess an elaborate flagellar apparatus which can involve up to tens of thousands of flagella. However, despite extensive research in recent years, it has yet to be established whether magnetotactic bacteria steer their flagellar motors in response to their alignment in magnetic fields. Symbiosis with magnetotactic bacteria has been proposed as the explanation for magnetoreception in some marine protists. Research is underway on whether a similar relationship may underlie magnetoreception in as well. The oldest unambiguous magnetofossils come from the Cretaceous chalk beds of southern England, though less certain reports of magnetofossils extend to 1.9 billion years old Gunflint Chert.
The cell achieves its height in the water column by synthesising gas vesicles. As the cell rises up, it is able to increase its carbohydrate load through increased photosynthesis. Too high and the cell will suffer photobleaching and possible death, however, the carbohydrate produced during photosynthesis increases the cell's density, causing it to sink. The daily cycle of carbohydrate build-up from photosynthesis and carbohydrate catabolism during dark hours is enough to fine-tune the cell's position in the water column, bring it up toward the surface when its carbohydrate levels are low and it needs to photosynthesis, and allowing it to sink away from the harmful UV radiation when the cell's carbohydrate levels have been replenished. An extreme excess of carbohydrate causes a significant change in the internal pressure of the cell, which causes the gas vesicles to buckle and collapse and the cell to sink out.
Large vacuoles are found in three genera of filamentous sulfur bacteria, the Thioploca, Beggiatoa and Thiomargarita. The cytosol is extremely reduced in these genera and the vacuole can occupy between 40 and 98% of the cell. The vacuole contains high concentrations of nitrate ions and is therefore thought to be a storage organelle. (2026). 9783540262053 ISBN 9783540262053
The Hawaiian bobtail squid lives in symbiosis with the bioluminescent bacteria Aliivibrio fischeri which inhabits a special light organ in the squid's mantle. The bacteria are fed sugar and amino acid by the squid and in return hide the squid's silhouette when viewed from below, counter-illuminating it by matching the amount of light hitting the top of the mantle. The squid serves as a model organism for animal-bacterial symbiosis and its relationship with the bacteria has been widely studied.
Vibrio harveyi is a rod-shaped, motile (via polar Flagellum) bioluminescent bacterium which grows optimally between . It can be found free-swimming in tropical marine waters, Commensalism in the gut microflora of marine animals, and as both a primary and opportunistic pathogen of a number of marine animals. It is thought to be the cause of the milky seas effect, where a uniform blue glow is emitted from seawater during the night. Some glows can cover nearly .
In 2000 a team of microbiologists led by Edward DeLong made a crucial discovery in the understanding of the marine carbon and energy cycles. They discovered a gene in several species of bacteria responsible for production of the protein rhodopsin, previously unheard of in bacteria. These proteins found in the cell membranes are capable of converting light energy to biochemical energy due to a change in configuration of the rhodopsin molecule as sunlight strikes it, causing the pumping of a proton from inside out and a subsequent inflow that generates the energy. Bacteria with Batteries, Popular Science, January 2001, Page 55. The archaeal-like rhodopsins have subsequently been found among different taxa, protists as well as in bacteria and archaea, though they are rare in complex multicellular organisms.
Research in 2019 shows these "sun-snatching bacteria" are more widespread than previously thought and could change how oceans are affected by global warming. "The findings break from the traditional interpretation of marine ecology found in textbooks, which states that nearly all sunlight in the ocean is captured by chlorophyll in algae. Instead, rhodopsin-equipped bacteria function like hybrid cars, powered by organic matter when available—as most bacteria are—and by sunlight when nutrients are scarce."
There is an astrobiology conjecture called the Purple Earth hypothesis which surmises that original life forms on Earth were retinal-based rather than chlorophyll-based, which would have made the Earth appear purple instead of green.
Endosymbiont bacteria are bacteria that live within the body or cells of another organism. Some types of cyanobacteria are endosymbiont and cyanobacteria have been found to possess genes that enable them to undergo nitrogen fixation.
Organisms typically establish a symbiotic relationship due to their limited availability of resources in their habitat or due to a limitation of their food source. Symbiotic, chemosynthetic bacteria that have been discovered associated with mussels ( Bathymodiolus) located near hydrothermal vents have a gene that enables them to utilize hydrogen as a source of energy, in preference to sulphur or methane as their energy source for production of energy.
Olavius algarvensis is a worm which lives in coastal sediments in the Mediterranean and depends on symbiotic bacteria for its nutrition. It lives with five different species of bacteria located under its cuticle: two sulfide-oxidizing, two sulfate-reducing and one Spirochaeta. The symbiotic bacteria also allow the worm to use hydrogen and carbon monoxide as energy sources, and to metabolise organic compounds like Malic acid and acetate.
Astrangia poculata, the northern star coral, is a temperate stony coral, widely documented along the eastern coast of the United States. The coral can live with and without zooxanthellae (algal symbionts), making it an ideal model organism to study microbial community interactions associated with symbiotic state. However, the ability to develop primers and Molecular probe to more specifically target key microbial groups has been hindered by the lack of full length 16S rRNA sequences, since sequences produced by the Illumina platform are of insufficient length (approximately 250 base pairs) for the design of primers and probes. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. In 2019, Goldsmith et al. demonstrated Sanger sequencing was capable of reproducing the biologically-relevant diversity detected by deeper next-generation sequencing, while also producing longer sequences useful to the research community for probe and primer design (see diagram on right). Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Most of the volume of the world ocean is in darkness. The processes occurring within the thin illuminated surface layer (the photic layer from the surface down to between 50 and 170 metres) are of major significance to the global biosphere. For example, the visible region of the solar spectrum (the so-called photosynthetically available radiation or PAR) reaching this sunlit layer fuels about half of the primary productivity of the planet, and is responsible for about half of the atmospheric oxygen necessary for most life on Earth. (1980). 9783662229880, Springer Berlin Heidelberg. ISBN 9783662229880
Heterotrophic bacterioplankton are main consumers of dissolved organic matter (DOM) in pelagic marine food webs, including the sunlit upper layers of the ocean. Their sensitivity to ultraviolet radiation (UVR), together with some recently discovered mechanisms bacteria have evolved to benefit from photosynthetically available radiation (PAR), suggest that natural sunlight plays a relevant, yet difficult to predict role in modulating bacterial biogeochemical functions in the oceans.
Ocean surface habitats sit at the interface between the atmosphere and the ocean. The biofilm habitat at the surface of the ocean harbours surface-dwelling microorganisms, commonly referred to as neuston. This vast air–water interface sits at the intersection of major air–water exchange processes spanning more than 70% of the global surface area . Bacteria in the surface microlayer of the ocean, called bacterioneuston, are of interest due to practical applications such as air-sea gas exchange of greenhouse gases, production of climate-active marine aerosols, and remote sensing of the ocean. Of specific interest is the production and degradation of (surface active materials) via microbial biochemical processes. Major sources of surfactants in the open ocean include phytoplankton, terrestrial runoff, and deposition from the atmosphere.
Unlike coloured algal blooms, surfactant-associated bacteria may not be visible in ocean colour imagery. Having the ability to detect these "invisible" surfactant-associated bacteria using synthetic aperture radar has immense benefits in all-weather conditions, regardless of cloud, fog, or daylight. This is particularly important in very high winds, because these are the conditions when the most intense air-sea gas exchanges and marine aerosol production take place. Therefore, in addition to colour satellite imagery, SAR satellite imagery may provide additional insights into a global picture of biophysical processes at the boundary between the ocean and atmosphere, air-sea greenhouse gas exchanges and production of climate-active marine aerosols.
The diagram on the right shows links among the ocean's biological pump and the pelagic food web and the ability to sample these components remotely from ships, satellites, and autonomous vehicles. Light blue waters are the euphotic zone, while the darker blue waters represent the Mesopelagic zone. Modified text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
Researchers recently discovered archaeal involvement in ammonia oxidation reactions. These reactions are particularly important in the oceans. In the sulfur cycle, archaea that grow by oxidizing sulfur compounds release this element from rocks, making it available to other organisms, but the archaea that do this, such as Sulfolobus, produce sulfuric acid as a waste product, and the growth of these organisms in abandoned mines can contribute to acid mine drainage and other environmental damage. In the carbon cycle, methanogen archaea remove hydrogen and play an important role in the decay of organic matter by the populations of microorganisms that act as in anaerobic ecosystems, such as sediments and marshes.
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