Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany.
Environ Microbiol. 2010 Apr;12(4):1041-52. doi: 10.1111/j.1462-2920.2009.02149.x. Epub 2010 Jan 26.
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.
脆杆藻是极地海冰中占主导地位的耐寒硅藻属。两种物种脆杆藻和短脆杆藻能够在海水冰点以下和平均以上的海水盐度下生长和分裂。在这里，我们表明，参与几种耐寒生物适应寒冷的抗冻蛋白（AFP）在这两个极地物种中广泛存在。 AFP 基因（afps）作为一个多基因家族的存在表明了该基因对脆杆藻属的重要性，可能有助于其在海冰中的成功。蛋白质系统发育表明 afps 的潜在迁移性，这些基因似乎跨越了王国和域的边界，存在于细菌、硅藻、甲壳类动物和真菌中。我们的研究结果表明，AFP 不仅在极地生物中广泛分布，而且在与寒冷环境明显无关的分类群中也广泛分布，这表明这些蛋白质可能具有多功能性。基因表达分析也表明了 AFP 对脆杆藻的重要性。在具有亚零温度和高盐度的典型海冰胁迫条件下，F. cylindrus 和 F. curta 强烈表达了选定的 afps。脆杆藻 AFP 中的 E/G 点突变可能在基因表达活性和蛋白功能中起作用。
