Active sulfur cycling by diverse mesophilic and thermophilic microorganisms in terrestrial mud volcanoes of A zerbaijan

Abstract

Summary Terrestrial mud volcanoes ( TMVs ) represent geochemically diverse habitats with varying sulfur sources and yet sulfur cycling in these environments remains largely unexplored. Here we characterized the sulfur‐metabolizing microorganisms and activity in four TMVs in A zerbaijan. A combination of geochemical analyses, biological rate measurements and molecular diversity surveys (targeting metabolic genes apr A and dsr A and SSU ribosomal RNA ) supported the presence of active sulfur‐oxidizing and sulfate‐reducing guilds in all four TMVs across a range of physiochemical conditions, with diversity of these guilds being unique to each TMV . The TMVs varied in potential sulfate reduction rates ( SRR ) by up to four orders of magnitude with highest SRR observed in sediments where in situ sulfate concentrations were highest. Maximum temperatures at which SRR were measured was 60° C in two TMVs . Corresponding with these trends in SRR , members of the potentially thermophilic, spore‐forming, D esulfotomaculum were detected in these TMVs by targeted 16 S rRNA analysis. Additional sulfate‐reducing bacterial lineages included members of the D esulfobacteraceae and D esulfobulbaceae detected by apr A and dsr A analyses and likely contributing to the mesophilic SRR measured. Phylotypes affiliated with sulfide‐oxidizing G amma ‐ and B etaproteobacteria were abundant in apr A libraries from low sulfate TMVs , while the highest sulfate TMV harboured 16 S rRNA phylotypes associated with sulfur‐oxidizing E psilonproteobacteria . Altogether, the biogeochemical and microbiological data indicate these unique terrestrial habitats support diverse active sulfur‐cycling microorganisms reflecting the in situ geochemical environment.

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