Molecular evidence for microorganisms participating in Fe, Mn, and S biogeochemical cycling in two low‐temperature hydrothermal fields at the Southwest Indian Ridge

Abstract

AbstractWe examined two low‐temperature hydrothermal deposits rich in Fe‐Si‐Mn collected from the recently discovered hydrothermal fields at the Southwest Indian Ridge using mineralogical, geochemical, and molecular biological techniques. The mineralogical and geochemical analyses indicated that the low‐temperature hydrothermal fields would provide a warm and chemical species‐rich habitat for chemosynthetic‐based hydrothermal ecosystems. Analyses of 16S rRNA sequences showed that ζ‐Proteobacteria, Pseudoalteromonas, Leptothrix, and Pseudomonas were potential Fe and Mn oxidizers in the low‐temperature hydrothermal environments, but they were not present in equal abundance among the subniches. Some potential Fe and Mn reducers were also recovered; they were more commonly found in the exterior black Fe‐Mn oxides. The difference between the exterior black Fe‐Mn oxides and the interior Opal‐A could be related to differences in in situ physicochemical conditions. We also identified microbial players that may participate in sulfur (S) geochemical cycling in these low‐temperature hydrothermal environments via analyses of 16S rRNA sequences and the aprA functional gene. The results indicated that members of γ‐Proteobacteria and α‐Proteobacteria were involved in the S oxidation process, while members of δ‐Proteobacteria, Nitrospirae, Firmicutes, and Archaea might participate in the S reduction process. Fe, Mn, and S oxidizers and reducers might actively participate in hydrothermal biogeochemical processes, which could influence the transfer of chemical species and the formation of biogenic minerals.