Biogenic elemental sulfur, S(0), is a key intermediate in global sulfur cycling, but relatively little is understood about its formation and composition. Both phototrophic and chemolithotrophic S-oxidizing microorganisms can form S(0) as an intermediate or final product. We are particularly interested in microbes that form extracellular S(0), as this is available for geochemical and ecological interactions, and may lead to geological sulfur deposits. We are studying three S-oxidizing isolates, the phototroph Chlorobaculum tepidum and chemolithotrophic Epsilonproteobacteria Sulfurimonas hongkongensis and Sulfuricurvum kujiense. C. tepidum forms S(0) globules at a distance from the cells, implying a soluble intermediate. Indeed, we detect polysulfide during S(0) formation. XRD and micro-Raman spectroscopy show the globules contain crystalline α-cyclo-octasulfur, while a range of analyses suggest that globule surfaces are enriched in organic carbon, likely affecting reactivity and bioaccessibility. The Epsilonproteobacteria isolate globules appear similar to C. tepidum globules. Experiments with these isolates are ongoing, but initial Raman spectroscopy results suggest that there is a precursor phase, prior to formation of crystalline α-cyclo-octasulfur. We have begun studies at the Frassasi Cave system in Italy, to follow S(0) formation by Epsilonproteobacteria Sulfurovumales streamers, which form at the air-water interface in a high sulfide (&gt;300 micromolar), low oxygen (~10 micromolar) stream, and contain up to 80% S(0) by weight. In a colonization experiment, biofilms formed within 3 days, and lush streamers by 7 days. We followed several biofilms for 11 days, performing field geochemical analyses and sampling biomass, minerals, and water for various lab analyses (microscopy, 16S rRNA, metagenome and transcriptomes, polysulfide, total sulfide, etc.). We will report on progress on both isolates and field sample analyses, toward a more specific mechanistic understanding of biogenic S(0) formation and persistence.

Elemental sulfur biomineralization by phototrophs and chemolithotrophs: Model isolate and field studies

253rd National Meeting (2017)

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