Photosynthetic purple sulfur bacteria (PSB) play crucial roles in the biogeochemical cycling of sulfur, carbon, metals, and oxygen. Despite their relevance in nature, their potential interactions with solid-phase substrates (i.e., metal sulfide nanoprecipitates) remain understudied and poorly understood which may lead to incomplete understanding of the cycling patterns of metals and sulfur. This study investigates the possibility of PSB using metal sulfide nanoparticles as sole electron donors for growth and metabolism. A. vinosum and H. halophila, which oxidize aqueous hydrogen sulfide into elemental sulfur globules either stored intracellularly or extracellularly, were selected as model strains for this study. A comparative approach is used to study the kinetics and mechanisms of the bacterial growth upon metal sulfide (i.e., NiS), with identical systems growing upon soluble sulfide as positive controls. Growth curve of positive controlled were tracked over time with IV-Vis at 600nm. In both control and NiS-amended cell culture media, substrate utilization rates were estimated through measuring the sulfide and sulfate concentrations in the media using a colorimetric assay and ion chromatography, respectively. In the NiS-samples, nickel concentrations were also tracked using ICP-MS. Preliminary results showed that growth in the positive control is faster with changes in sulfide concentration in PPM for compared to PPB changes for NiS supported bacteria, thus NiS cultures supported a much smaller bacterial density as evaluated visually. Changes in sulfide concentrations are undetectable in the NiS system, suggesting either sulfide is utilized as soon as it becomes available or different utilization mechanisms are involved, which are to be resolved through comparative transcriptomic analysis of bacterial cells grown upon different sulfur sources.

Utilization of solid-phase metal sulfide as electron donors by <i>A. vinosum</i> and <i>H. halophila</i>: A comparative and mechanistic study

ACS Fall 2021

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Utilization of solid-phase metal sulfide as electron donors by A. vinosum and H. halophila: A comparative and mechanistic study