Microbial community and genomic insight to predominant candidatus Atribacteria JS1 lineage in marine sediments of the Ross Sea, Antarctica

Abstract

The microbial biomass of the subseafloor with majority of uncultivated candidate phyla plays an important role in global biogeochemical cycles. Candidate phylum Atribacteria JS1 is among the predominant members in anoxic subseafloor environments, especially in methane-rich sediments. However, the metabolic potential and biogeochemical role of this phylum have remained elusive due to the lack of axenic culture representatives. Here, weinvestigated the microbial communities of marine sediments of the Ross Sea, Antarctica and genomic features of candidate phylum Atribacteria JS1. Candidate phyla accounted for 21.4？56.2% of bacterial communities, with Atribacteria JS1 as the most abundant candidate phylum (9.0？39.6%). Genomic analysis revealed that 18 single-cell amplified genomes (SAGs) of Atribacteria JS1were from a single species with a high 16S rRNA gene similarity (> 99.3%) and average nucleotide identity value (>96.8%). The composite genome constructed by co-assembly showed the highest genome coverage among Atribacteria JS1 genomes. Atribacteria JS1 was predicted to be a homoacetogenic bacterium capable of growing on H2/CO2 or CO2, with a heterotrophic lifestyle. The presence of the Wood-Ljungdahl pathway suggested that Atribacteria JS1 may be a syntrophic acetate-oxidizer explaining the high abundance of this group in anoxic methane-rich sediments. These data expand our knowledge of Atribacteria JS1 and the ecological function of this uncultivated group in carbon cycling.