title: Antifreeze proteins in polar sea ice diatoms: diversity and gene expression in the genus Fragilariopsis.
abstract: Fragilariopsis is a dominating psychrophilic diatom genus in polar sea ice. The two species Fragilariopsis cylindrus and Fragilariopsis curta are able to grow and divide below freezing temperature of sea water and above average sea water salinity. Here we show that antifreeze proteins (AFPs), involved in cold adaptation in several psychrophilic organisms, are widespread in the two polar species. The presence of AFP genes (afps) as a multigene family indicated the importance of this group of genes for the genus Fragilariopsis, possibly contributing to its success in sea ice. Protein phylogeny showed the potential mobility of afps, which appear to have crossed kingdom and domain borders, occurring in Bacteria, diatoms, crustaceans and fungi. Our results revealed a broad distribution of AFPs not only in polar organisms but also in taxa apparently not related to cold environments, suggesting that these proteins may be multifunctional. The relevance of AFPs to Fragilariopsis was also shown by gene expression analysis. Under stress conditions typical for sea ice, with subzero temperatures and high salinities, F. cylindrus and F. curta strongly expressed selected afps. An E/G point mutation in the Fragilariopsis AFPs may play a role in gene expression activity and protein function.
authors.affiliation: Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany. maddalena.bayer@awi.de
authors.forename: Maddalena
authors.initials: M
authors.lastname: Bayer-Giraldi
authors.forename: Christiane
authors.initials: C
authors.lastname: Uhlig
authors.forename: Uwe
authors.initials: U
authors.lastname: John
authors.forename: Thomas
authors.initials: T
authors.lastname: Mock
authors.forename: Klaus
authors.initials: K
authors.lastname: Valentin
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism*; D021301:Antifreeze Proteins / Q000235:genetics / Q000378:metabolism*; D003080:Cold Temperature; D048028:DNA, Algal / Q000235:genetics; D017377:Diatoms / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D046448:Ice Cover / Q000382:microbiology; D010802:Phylogeny; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D012623:Seawater / Q000382:microbiology*; D017422:Sequence Analysis, DNA
chemical_list: D020418:Algal Proteins; D021301:Antifreeze Proteins; D048028:DNA, Algal; D020033:Protein Isoforms