Metagenomic analyses of a microbial assemblage in a subglacial lake beneath the Vatnajokull ice cap, Iceland

Skaftarkatlar are two subglacial lakes located beneath the Vatnajokull 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.

Automated summary

This study analyzed the microbial ecology of the Skaftarkatlar subglacial lakes in Iceland, revealing a low-diversity core microbial assemblage and the dominance of chemolithoautotrophy as the main metabolism. These findings highlight the importance of in situ investigations in understanding this unique environment, as they are not reflected in enrichment cultures.