Microbial consumption of zero-valence sulfur in marine benthic habitats

Zero-valence sulfur (S⁰) is a central intermediate in the marine sulfur cycle and forms conspicuous accumulations at sediment surfaces, hydrothermal vents and in oxygen minimum zones. Diverse microorganisms can utilize S⁰, but those consuming S⁰ in the environment are largely unknown. We identified possible key players in S⁰ turnover on native or introduced S⁰ in benthic coastal and deep-sea habitats using the 16S ribosomal RNA approach, (in situ) growth experiments and activity measurements. In all habitats, the epsilonproteobacterial Sulfurimonas/Sulfurovum group accounted for a substantial fraction of the microbial community. Deltaproteobacterial Desulfobulbaceae and Desulfuromonadales were also frequently detected, indicating S⁰ disproportionation and S⁰ respiration under anoxic conditions. Sulfate production from S⁰ particles colonized in situ with Sulfurimonas/Sulfurovum suggested that this group oxidized S⁰. We also show that the type strain Sulfurimonas denitrificans is able to access cyclooctasulfur (S₈), a metabolic feature not yet demonstrated for sulfur oxidizers. The ability to oxidize S⁰, in particular S₈, likely facilitates niche partitioning among sulfur oxidizers in habitats with intense microbial sulfur cycling such as sulfidic sediment surfaces. Our results underscore the previously overlooked but central role of Sulfurimonas/Sulfurovum group for conversion of free S⁰ at the seafloor surface.