Polaribacter
Polaribacter is a genus from the family of Flavobacteriaceae. They are gram-negative, aerobic bacteria that can be heterotrophic, psychrophilic or mesophilic. Most species are non-motile and species range from ovoid to rod-shaped. "Polaribacter" forms yellow- to orange-pigmented colonies. They have been mostly adapted to cool marine ecosystems and their optimal growth range is at a temperature between 10-32 °C and at a pH of 7.0-8.0. They are oxidase and catalase-positive and are able to grow from carbohydrates, amino acids, and organic acids. There is evidence of two life strategies for "Polaribacter . Some species have evolved to a free-living lifestyle where amino acids and carbohydrates are consumed. Polaribacter" with this lifestyle have proteorhodopsin that enhances living in oligotrophic seawaters. Other species of "Polaribacter" attach to substrate in search of protein polymers. In the context of climate change, algal blooms are becoming increasingly prevalent. Polaribacter's role as a decomposer of algal cells may be important as seawater chemistry and microbial composition is altered as temperatures continue to rise. This may impact the efficiency of biological pumps in sequestering atmospheric carbon. "Polaribacter" is a genus that is being continuously researched and to  date there are 25 species that have been validly published under the International Code of Nomenclature of Prokaryotes (ICNP): "P. aquimarinus, P. atrinae," "P. butkevichii", "P. dokdonensis", "P. filamentus", "P. franzmannii", "P. gangjinensis, P. glomeratus", "P. haliotis, P. huanghezhanensis, P. insulae, P. irgensii, P. lacunae, P. litorisediminis, P. marinaquae, P. marinivivus, P. pacificus, P. porphyrae, P. reichenbachii, P. sejongensis, P. septentrionalilitoris, P. staleyi, P. tangerinus, P. undariae, P. vadi." When referring to more than one species, the plural is Polaribacteria. Phylogeny. This phylogeny is based on rRNA gene sequencing. Distribution and Abundance. "Polaribacter" are abundant in polar oceans and are  important in the export of dissolved organic matter (DOM). A small percentage of the bacterial community is responsible for the DOM uptake rate. In northern latitude waters, the fraction of cells using glucose (fraction of active cells) is higher in summer than winter,and high abundance is seen after a phytoplankton bloom. In southern latitude waters, one study found lower "Polaribacter" abundance after an "in situ" diatom bloom. Within the Arctic Ocean, there is no obvious pattern in the relative abundance between summer and winter. In the Chukchi Sea, the fraction cells using leucine is higher in the winter than  in summer. In the Beaufort Sea, the fraction of cells using leucine does not differ between seasons. In the coastal waters of Fildes Peninsula, "Polaribacter" dominated the Bacteriodetes population. Habitat. P"olaribacter" are widely distributed microorganisms and various species are capable of living in a plethora of different environments. Some "Polaribacter" species have been isolated from brine pools in the Arctic Ocean. in addition to hypersaline environments, numerous "Polaribacter" species inhabit extreme environments ranging from -20 °C to 22 °C. In the past, it was thought that "Polaribacter" only flourished in cold waters as the species first discovered ("P.  irgensii, P. filamentus," and "P. franzmannii") in the Arctic and Antarctic Sea could only survive in water with temperatures ranging from -20 °C to 10 °C. "Polaribacter" are very versatile microorganisms and can survive in oligotrophic and in copiotrophic environments. "Polaribacter" have also been found in sediments. For example, a research study was executed where they were able to isolate a very phylogenetically close strain to "Polaribacter" called SM1202T from marine sediment in Kongsfjorden, Svalbard. "Polaribacter" have also been experimentally isolated from red macroalgae ("Porphyra yezoensis) a"nd Pacific green macroalgae ("Ulva fenestrate)". Role in ecosystem. Isolated samples  show that Flavobacteria are well-developed to degrade High-Molecular Weight (HMW) DOM."Polaribacter" may be among the first organisms to degrade particulate organic matter and break-down polymers into smaller particles that can be used by free-living bacterial heterotrophs. This suggests that they likely remineralize primary production matter within the food web. In the southern ocean. The Antarctic Peninsula exhibits strong seasonal changes, which influences how bacteria respond to and live in these environmental conditions. The Antarctic spring is especially important as it brings about significant changes, including sea ice melting, thermal stratification due to warming surface waters, and  increased dissolved organic matter (DOM) production. All these physical changes also result in phytoplankton blooms which are important in supporting higher trophic levels. In the Southern Ocean, Flavobacteria dominate bacterial activity, particularly Flavobacteria of the "Polaribacter" genus. Typically, these bacteria are prevalent in sea ice, however, during seasonal melting in the summer, they dominate coastal waters as sea ice retreats. In the Southern Ocean, when phytoplankton blooms occur, Flavobacteria, and particularly "Polaribacter," are among the first bacterial taxa to respond to phytoplankton blooms and break down organic matter by direct attachment and the use of exoenzymes. Both particle-attached and  free-living members of Rhodobacteraceae were also found in close association of the phytoplankton blooms, however, bacterium from this family were found to utilize lower molecular weight substrates. This suggests that they’re secondary in the microbial succession of substrates, utilizing the byproducts of degradation by Flavobacteria. The relative abundance of free-living "Polaribacter" and Rhodobacteraceae was found to peak at different points during the phytoplankton blooms, suggesting a niche specialization contributing to successive degradation of phytoplankton-derived organic matter. "Polaribacter" and Rhodobacteraceae were found in clusters, with "Polaribacter" clusters forming earlier on in the bloom which further suggests a  successive ecological interaction between various bacterial taxa. For both the Arctic Oceans and the North Sea, "Polaribacter" exhibited similar trends pertaining to phytoplankton blooms in the summertime as well as assuming particular niches for organic matter degradation. Metabolism. "Polaribacter" are metabolically flexible depending on their physiologies, lifestyle and seasonality of the region they inhabit. Many research studies have found that "Polaribacter" can alternate between two lifestyles as a mechanism for adaptation in surface waters where nutrient concentrations are low and light exposure is high. Sequenced strains of "Polaribacter" show a high prevalence of peptidase and glycoside hydrolase genes in comparison  to other Flavobacteriaceae, indicating they contribute to degradation and uptake of external proteins and oligopeptides. In the pelagic water column, some species are well equipped to attach to particles and substrates to search for and degrade polymers. They are amongst the first organisms to degrade particulate organic matter and break-down polymers into smaller particles. Studies have shown that they will colonize and attach to particles, glide to search for substrates, and degrade them for carbon and nutrients. Once they’ve degraded these molecules,  the bacterium may then search for new particles to colonize, forcing them to freely-swim in  environments where nutrients and organic carbon is not easily available. CAZymes. Genetic sequencing found that strains contain numerous genes which encode for CAZymes that are involved in polysaccharide degradation. For example, strain DSW-5 (a strain genetically very similar to strain MED-152), contains 85 genes encoding to CAZymes and 203 peptidases, which suggests its role as a free-living heterotrophs. However, the ratio of peptidases to glycoside hydrolase genes varies depending on the environmental conditions the strain is subjected to. For example, "Polaribacter" sp. MED134 lives in environmental conditions with extended starvation conditions and expresses twice as many peptidases as CAZymes . On the other hand, macroalgae-colonizing species that live in stable, eutrophic environments may express greater proportions of CAZymes than peptidases. Proteorhodopsin. "Free-living" species have the proteorhodopsin gene, which allows them to complete inorganic-carbon fixation using light as an energy source. By utilizing their proteorhodopsin to use light energy, "Polaribacter" can grow in oligotrophic environmental conditions. Genome. General Genome Characteristics. The "Polaribacter" genome varies in genome size (2.76 Mb ("P. irgensii") - 4.10 Mb ("P. reichenbachii")) and number of genes (2446 "(P. irgensii") - 3500 ("P. reichenbachii")) but has a fairly constant G+C content of approximately 30 mol%. Some notable  features of the genome include the presence of agar, alginate, and carrageenan degrading enzymes in "Polaribacter" species which colonize the surface of macroalgae. Agar degrading enzymes have also been found in Polaribacter strains that colonize the gut of the comb pen shell. Proteases are also commonly found in the genomes of species, which preferentially grow on solid substrates and degrade protein instead of using free amino acids and living a pelagic lifestyle. Some members of the genus encode proteorhodopsin, which has been implicated in supporting their central metabolism through photophosphorylation. DNA Sequencing of "Polaribacter". Due to their relatively modern discovery , DNA sequencing has commonly been used to identify new strains of "Polaribacter" and help place species on a phylogenetic tree. DNA sequencing has also been used to help understand, or predict a species role in an environment due to the presence of certain genes. Members of the family Flavobacteriaceae can be identified through a specific quinone called Menaquinone 6 also known as Vitamin K2, however differentiating the species can be much more difficult. Species such as "Polaribacter vadi" and "Polaribacter atrinae" were identified as new species based on their similar but unique genome when compared to other members of the  Polaribacter genus. New species can be identified through DNA hybridization or through the sequencing and comparison of a common gene such as 16S rRNA. This has allowed scientists to create phylogenetic trees of the genus based on genomic similarity, as seen in the phylogeny section, as well as identify common features in the genome. Life Strategies of "Polaribacter" Based on Genome Analysis. Genomic analysis on its own has allowed scientist to examine the relationships between different species of "Polaribacter". However by combining genomic analysis with other analytical techniques such as chemotaxonomic and biochemical, scientists can theorize how a species might  fit into an environment or how they believe a species is adapted to survive. A genomic analysis of the "Polaribacter" strain MED152, found a considerable amount of genes that allow for surface or particle attachment, gliding motility and polymer degradation. These genes fit with the current understanding of how marine bacteroidetes survive through attaching to a surface and moving over it to look for nutrients. However the researchers also noticed that the organism had a proteorhodopsin gene as well as other genes which could be used to sense light and found that under light the species increased carbon dioxide fixation . This led the researchers to theorize that "Polaribacter" strain MED152 has two different life strategies, one where it acts like other marine bacteroidetes, attaching to surfaces and searching for nutrients and, another life strategy where, if the strain was in a well lit, low nutrient area of the ocean, it would use carbon fixation to synthesize intermediates of metabolic pathways. Another example of this comes from the "Polaribacter" strains Hel1_33_49 and Hel1_85. The strain Hel1_33_49 has a genome which contains proteorhodopsin, fewer polysaccharide utilization loci and no mannitol dehydrogenase, which the researchers associate with a pelagic lifestyle. Hel1_85 on the  other hand, has a genome which contains twice as many polysaccharide utilization loci, a mannitol dehydrogenase and no proteorhodopsin, pointing to a lifestyle with lower oxygen availability such as a biofilm. Viral pathogens. Only two species of lytic phage are known to infect members of this genus so far, and both have double stranded DNA with virions that include isometric heads and non-contractile tails. Viral lysis has been implicated as a major driver of changes in genus-level composition of microbial communities. Applications/uses. Cold water enzymes contained in psychrophilic bacteria like "Polaribacter" are valuable for biotechnology applications since  they do not require high temperatures that may other enzyme systems do. Psychrophilic enzymes. "Polaribacter" is a psychrophilic bacterium that lends itself to a variety of applications in both academic and industrial settings. These cold dwelling bacteria are an abundant source of psychrophilic enzymes which have an interesting ability to retain higher catalytic activity at temperatures below 25°C. This is due to the highly malleable nature of these enzymes as this allows for better substrate - active site binding at colder temperatures. This is important as enzymes that operate at lower temperatures not only make the industrial processes more  efficient, but they also minimize the chance of side reactions occurring. More of the substrate can directly be converted into the desired product all the while requiring less energy to do so. Psychrophilic enzymes can also aid with heat labile or volatile compounds, allowing reactions to occur without significant product loss. Another unique application for these enzymes is the ability to be inhibited without the need of external reagents. Usually to stop enzyme activity, chemical inhibitors are required which then require subsequent purification steps. With psychrophilic enzymes you can add slight heat to prevent any further reaction from occurring. Psychrophilic  proteases derived from "Polaribacter" can be added to detergents allowing the washing of fabric at room temperature. An example of this is the enzyme carrageenase, which has been shown to have anti-tumor, antiviral, antioxidant and immunomodulatory activities. However, carrageenase isolated from bacteria has historically had low enzyme activity and poor stability. Recently researchers have isolated and cloned the carrageenase gene from the "Polaribacter sp." NJDZ03, which shows better thermostability, and the ability to be active at lower temperatures, making it a better choice for industrial uses. Exopolysaccharide. EPS is a secreted exopolysaccharide which protects the cells, stabilizes membranes, and  serve and carbon stores. Most EPS is similar but it is found that in extremophiles, the composition may be distinct. Specifically in Polaribacter sp. SM1127, where the EPS has antioxidant activity and has shown to protect human fibroblast cells at lower temperatures. Studies by Sun et al. were done to determine whether this can be utilized to protect and repair damage caused by frostbite. It was found that "Polaribacter" derived EPS helps facilitate the dermal fibroblast cell movement to the site of injury. This not only promotes healing during frostbite injury but other cutaneous wounds as well/