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Metal sulfide minerals, including mercury sulfides (HgS), are widespread in hydrothermal vent systems where sulfur‐oxidizing microbes are prevalent. Questions remain as to the impact of mineral composition and structure on sulfur‐oxidizing microbial populations at deep‐sea hydrothermal vents, including the possible role of microbial activity in remobilizing elemental Hg from HgS. In the present study, metal sulfides varying in metal composition, structure, and surface area were incubated for 13 days on and near a diffuse‐flow hydrothermal vent at 9°50′N on the East Pacific Rise. Upon retrieval, incubated minerals were examined by scanning electron microscopy with energy‐dispersive X‐ray spectroscopy (SEM‐EDS), X‐ray diffraction (XRD), and epifluorescence microscopy (EFM). DNA was extracted from mineral samples, and the 16S ribosomal RNA gene sequenced to characterize colonizing microbes. Sulfur‐oxidizing genera common to newly exposed surfaces (Sulfurimonas, Sulfurovum, and Arcobacter) were present on all samples. Differences in their relative abundance between and within incubation sites point to constraining effects of the immediate environment and the minerals themselves. Greater variability in colonizing community composition on off‐vent samples suggests that the bioavailability of mineral‐derived sulfide (as influenced by surface area, crystal structure, and reactivity) exerted greater control on microbial colonization in the ambient environment than in the vent environment, where dissolved sulfide is more abundant. The availability of mineral‐derived sulfide as an electron donor may thus be a key control on the activity and proliferation of deep‐sea chemosynthetic communities, and this interpretation supports the potential for microbial dissolution of HgS at hydrothermal vents.

Chemoautotrophic bacteria belonging to the genusSulfurimonas(classCampylobacteria) were previously identified as key players in the turnover of zero‐valence sulfur, a central intermediate in the marine sulfur cycle.S. denitrificanswas further shown to be able to oxidize cyclooctasulfur (S₈). However, at present the mechanism of activation and metabolism of cyclooctasulfur is not known. Here, we assessed the transcriptome and proteome ofS. denitrificansgrown with either thiosulfate or S₈as the electron donor. While the overall expression profiles under the two growth conditions were rather similar, distinct differences were observed that could be attributed to the utilization of S₈. This included a higher abundance of expressed genes related to surface attachment in the presence of S₈, and the differential regulation of the sulfur‐oxidation multienzyme complex (SOX), which inS. denitrificansis encoded in two gene clusters:soxABXY₁Z₁andsoxCDY₂Z₂. While the proteins of both clusters were present with thiosulfate, only proteins of thesoxCDY₂Z₂were detected at significant levels with S₈. Based on these findings a model for the oxidation of S₈is proposed. Our results have implications for interpreting metatranscriptomic and ‐proteomic data and for the observed high level of diversification ofsoxY₂Z₂among sulfur‐oxidizingCampylobacteria.