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

Abstract

[1] We 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 z-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 g-Proteobacteria and a-Proteobacteria were involved in the S oxidation process, while members of d-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.

The Size Fractionation and Speciation of Iron in the Longqi Hydrothermal Plumes on the Southwest Indian Ridge

“…It was found that there were no significant differences in microbial compositions between the hydrothermal plume samples and the ambient seawater (Li et al, ). Nevertheless, microorganisms (including bacterial and archaea) such as Fe, Mn, S oxidizers and reducers, and membrane lipids were abundant in the low‐temperature diffuse environment (Li et al, ; Pan et al, ; Peng et al, ). Therefore, organic matter from the nearby diffuse flow might be the most likely source of the ligands in Longqi hydrothermal plumes.…”

Coexistence of Fe(II)- and Mn(II)-oxidizing bacteria govern the formation of deep sea umber deposits

“…Recently, much research has gone into an understanding of sedimentation on ocean ridges, especially metalliferous sediments generated by activity of submarine hydrothermal systems (Dekov et al, 2010;Edwards et al, 2011;Peng et al, 2011;Li et al, 2013). Hydrothermal umber deposits are fossiliferous, siliceous fine-grained, Fe-Mn-rich sediments.…”

230Th/238U dating of hydrothermal sulfides from Duanqiao hydrothermal field, Southwest Indian Ridge

“…Niu et al (2015) also identified the thick crust (*10 km) beneath the segment center by wide-angle seismic reflection. Li et al (2013) reported the geochemical and molecular biological compositions of low-temperature hydrothermal deposits. Sun et al (2015) further investigated the mineralization of these deposits indicating the presence of Fe-oxidizing bacteria.…”