Polaribacter is a genus in the family 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 and 32 °C and at a pH of 7.0 to 8.0. They are oxidase and catalase-positive and are able to grow using carbohydrates, amino acids, and organic acids. There is evidence of two life strategies for members of the genus, Polaribacter. Some Polaribacter species are free-living and consume amino acids and carbohydrates, as well as have proteorhodopsin that enhances living in oligotrophic seawaters. Other species of Polaribacter attach to substrates in search of protein polymers. In the context of climate change, algal blooms are becoming increasingly prevalent. Members of the genus Polaribacter decompose algal cells and thus may be important in biogeochemical cycling, as well as influence seawater chemistry and the composition of microbial communities as temperatures continue to rise. This may impact the efficiency of the biological pump 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. The genus is sometimes incorrectly referred to as Polaribacer; Polarobacter or Polaribacteria.
Phylogeny This phylogeny is based on rRNA gene sequencing.
Distribution and abundance Members in the genus 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 abundances may occur after phytoplankton blooms, although a study in southern high-latitude waters found lower abundances of Polaribacter 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 of 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 cells in the phylum Bacteriodetes.
Habitat
Microorganisms in the genus Polaribacter are widely distributed 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 members of the species that were first discovered (P. irgensii, P. filamentus, and P. franzmannii) in the Arctic and Southern Oceans could only survive in water with temperatures ranging from -20 °C to 10 °C. Subsequently, members of the genus Polaribacter have been shown to be very versatile microorganisms and can survive in oligotrophic and in copiotrophic environments. Polaribacter have also been found in sediments. For example, SM1202T, a phylogenetically close strain to Polaribacter was isolated from marine sediment in Kongsfjorden, Svalbard. Polaribacter have also been experimentally isolated from red macroalgae (Porphyra yezoensis) and green macroalgae (Ulva fenestrate).
Role in ecosystem Isolates of related Flavobacteria are able to degrade High-Molecular Weight (HMW) DOM. and 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.
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