Diverse sulfur metabolisms from two subterranean sulfidic spring systems.

In sulfidic environments, microbes oxidize reduced sulfur compounds via several pathways. We used metagenomics to investigate sulfur metabolic pathways from microbial mat communities in two subterranean sulfidic streams in Lower Kane Cave, WY, USA and from Glenwood Hot Springs, CO, USA. Both unassembled and targeted recA gene assembly analyses revealed that these streams were dominated by Epsilonproteobacteria and Gammaproteobacteria, including groups related to Sulfurovum, Sulfurospirillum, Thiothrix and an epsilonproteobacterial group with no close cultured relatives. Genes encoding sulfide:quinone oxidoreductase (SQR) were abundant at all sites, but the specific SQR type and the taxonomic affiliation of each type differed between sites. The abundance of thiosulfate oxidation pathway genes (Sox) was not consistent between sites, although overall they were less abundant than SQR genes. Furthermore, the Sox pathway appeared to be incomplete in all samples. This work reveals both variations in sulfur metabolism within and between taxonomic groups found in these systems, and the presence of novel epsilonproteobacterial groups.