Cold environments impose challenges to organisms. Polyextremophile microorganisms can survive in these conditions thanks to an array of counteracting mechanisms. Naganishia vishniacii, a yeast species hitherto only isolated from McMurdo Dry Valleys, Antarctica, is an example of a polyextremophile. Here we present the first draft genomic sequence of N. vishniacii. Using comparative genomics, we unraveled unique characteristics of cold associated adaptations. 336 putative genes (total: 6183) encoding solute transfers and chaperones, among others, were absent in sister species. Among genes shared by N. vishniacii and its closest related species we found orthologs encompassing possible evidence of positive selection (dN/dS > 1). Genes associated with photoprotection were found in agreement with high solar irradiation exposure. Also genes coding for desaturases and genomic features associated with cold tolerance (i.e. trehalose synthesis and lipid metabolism) were explored. Finally, biases in amino acid usage (namely an enrichment of glutamine and a trend in proline reduction) were observed, possibly conferring increased protein flexibility. To the best of our knowledge, such a combination of mechanisms for cold tolerance has not been previously reported in fungi, making N. vishniacii a unique model for the study of the genetic basis and evolution of cold adaptation strategies.

中文翻译：

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Naganishia vishniacii 冷适应的独特基因组特征，一种从南极洲分离的多嗜极端酵母

寒冷的环境给生物体带来了挑战。多亏了一系列对抗机制，多嗜极端微生物可以在这些条件下存活。Naganishia vishniacii是一种迄今为止仅从南极洲麦克默多干谷分离出来的酵母物种，是多极端微生物的一个例子。在这里，我们展示了N. vishniacii 的基因组序列初稿。使用比较基因组学，我们揭示了寒冷相关适应的独特特征。336 个假定的基因（总共：6183 个）编码溶质转移和分子伴侣等，在姐妹物种中不存在。在N. vishniacii及其最亲缘物种共享的基因中，我们发现了包含正选择可能证据的直系同源物 ( dN/dS > 1)。发现与光保护相关的基因与高太阳辐射暴露一致。还探索了编码去饱和酶的基因和与耐寒性相关的基因组特征（即海藻糖合成和脂质代谢）。最后，观察到氨基酸使用的偏差（即谷氨酰胺的富集和脯氨酸减少的趋势），可能会增加蛋白质的灵活性。据我们所知，这种耐寒机制的组合以前在真菌中没有报道过，这使得N. vishniacii成为研究冷适应策略的遗传基础和进化的独特模型。