Sulfur and hydrogen metabolism linked to CO fixation by abundant Nitrospirae in the deep subsurface

天野 由記; Anantharaman, K.*; Tomas, B. C.*; Olm, M.*; Burstein, D.*; Castelle, C. J.*; 別部 光里*; 宮川 和也; 岩月 輝希; 鈴木 庸平*; et al.

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The bacterial phylum Nitrospirae is phylogenetically diverse. There are relatively few isolated representatives available for laboratory study and the physiology, functions and distributions of these bacteria across environments remain largely unknown. To understand the ecological role of Nitrospirae in the deep subsurface, we analyzed metagenomically-derived near complete genomes from groundwaters associated with granite and sedimentary rock where Nitrospirae are very abundant. The bacteria are autotrophs that fix CO via the Wood-Ljungdahl pathway and reductive TCA cycles. The genomes encode versatile energy-generating pathways that involve sulfate reduction, hydrogen oxidation and nitrite reduction. Phylogenetic analyses indicate that the organisms are most similar to the isolated magnetotactic bacterium, Candidatus Magnetobacterium bavaricum, with only 89-91% 16S rRNA gene sequence identity. These Nitrospirae bacteria appear to play critical ecosystem roles as primary producers and they are likely central to sulfur cycling in the deep subsurface.