Table_1_Metagenomic analyses of a microbial assemblage in a subglacial lake beneath the Vatnajökull ice cap, Iceland.DOCX

Skaftárkatlar are two subglacial lakes located beneath the Vatnajökull ice cap in Iceland associated with geothermal and volcanic activity. Previous studies of these lakes with ribosomal gene (16S rDNA) tag sequencing revealed a limited diversity of bacteria adapted to cold, dark, and nutrient-poor waters. In this study, we present analyses of metagenomes from the lake which give new insights into its microbial ecology. Analyses of the 16S rDNA genes in the metagenomes confirmed the existence of a low-diversity core microbial assemblage in the lake and insights into the potential metabolisms of the dominant members. Seven taxonomic genera, Sulfuricurvum, Sulfurospirillum, Acetobacterium, Pelobacter/Geobacter, Saccharibacteria, Caldisericum, and an unclassified member of Prolixibacteraceae, comprised more than 98% of the rDNA reads in the library. Functional characterisation of the lake metagenomes revealed complete metabolic pathways for sulphur cycling, nitrogen metabolism, carbon fixation via the reverse Krebs cycle, and acetogenesis. These results show that chemolithoautotrophy constitutes the main metabolism in this subglacial ecosystem. This assemblage and its metabolisms are not reflected in enrichment cultures, demonstrating the importance of in situ investigations of this environment.

斯卡特亚卡特拉尔湖（Skaftárkatlar）是位于冰岛瓦特纳冰原（Vatnajökull ice cap）下方的两座冰下湖，与地热及火山活动密切相关。过往针对这些湖泊开展的核糖体基因（16S rDNA）标签测序研究显示，适应寒冷、无光且营养匮乏水体的细菌多样性有限。本研究针对该湖的宏基因组展开分析，为其微生物生态学研究提供了全新视角。对宏基因组中16S rDNA基因的分析证实，该湖存在低多样性的核心微生物群落，并揭示了优势类群的潜在代谢模式。共计7个分类学属——硫弯菌属（Sulfuricurvum）、硫螺旋菌属（Sulfurospirillum）、产乙酸菌属（Acetobacterium）、Pelobacter属/地杆菌属（Geobacter）、糖细菌属（Saccharibacteria）、Caldisericum属，以及长杆菌科（Prolixibacteraceae）的1个未分类成员——其16S rDNA测序读长占文库总读长的98%以上。对湖泊宏基因组的功能注释分析显示，其存在完整的硫循环、氮代谢、基于反向三羧酸循环（reverse Krebs cycle）的固碳途径，以及产乙酸代谢通路。上述结果表明，化能自养型代谢是该冰下生态系统的主要代谢方式。该微生物群落及其代谢模式无法在富集培养体系中得以重现，这凸显了针对该环境开展原位研究的重要性。