Analysis of a multifunctional thiosulfate reductase and its regulation in Shewanella oneidensis MR-1.

摘要

Shewanella oneidensis MR-1 is a metal-reducing bacterium that uses a large number of electron acceptors for respiration, including oxygen, insoluble metal oxides, dimethyl sulfoxide (DMSO), nitrate, and fumarate. In addition, S. oneidensis MR-1 is capable of reducing thiosulfate (S2O3) and other sulfur compounds during anaerobic respiration. The mechanisms of sulfur reduction and its regulation are not well understood and have not been studied in detail in S. oneidensis MR-1. Unlike Salmonella which produces separate enzymes for the reduction of S2O3 or tetrathionate (S4O6), S. oneidensis appears to produce a single enzyme complex responsible for the reduction of multiple sulfur compounds. A mutation in genes encoding a polysulfide reductase complex, PsrABC, led to a complete loss of S2O3 reduction and a severe decrease in the reduction of S4O6. To further characterize PsrABC, identify components involved in electron transport to S2O 3 and S4O6, and evaluate the regulation of sulfur reduction, additional mutants were isolated and analyzed. Our findings suggest PsrABC is a molybdenum-containing enzyme secreted by the twin-arginine transfer secretion system. Electron transport to PsrABC requires menaquinones, but not c-cytochromes. In addition, the S. oneidensis thiosulfate respiratory pathway appears to be regulated by both CRP and a two-component regulatory system, TsaS and TsaR. Our results indicate that PsrABC is wholly responsible for thiosulfate reduction in S. oneidensis MR-1. Additionally, this enzyme appears to play a major role in the reduction of tetrathionate, trithionate, and polysulfide.