Endogenous generation of hydrogen sulfide and its regulation in Shewanella oneidensis

Abstract

Hydrogen sulfide (H2S) has been recognized as a physiological mediator with a variety of functions across all domains of life. In this study, mechanisms of endogenous H2S generation in Shewanella oneidensis were investigated. As a research model with highly diverse anaerobic respiratory pathways, the microorganism is able to produce H2S by respiring on a variety of sulfur-containing compounds with SirACD and PsrABC enzymatic complexes, as well as through cysteine degradation with three enzymes, MdeA, SO_1095, and SseA. We showed that the SirACD and PsrABC complexes, which are predominantly, if not exclusively, responsible for H2S generation via respiration of sulfur species, do not interplay with each other. Strikingly, a screen for regulators controlling endogenous H2S generation by transposon mutagenesis identified global regulator Crp to be essential to all H2S-generating processes. In contrast, Fnr and Arc, two other global regulators that have a role in respiration, are dispensable in regulating H2S generation via respiration of sulfur species. Interestingly, Arc is involved in the H2S generation through cysteine degradation by repressing expression of the mdeA gene. We further showed that expression of the sirA and psrABC operons is subjected to direct regulation of Crp, but the mechanisms underlying the requirement of Crp for H2S generation through cysteine degradation remain elusive.

A Matter of Timing: Contrasting Effects of Hydrogen Sulfide on Oxidative Stress Response in Shewanella oneidensis

“…S. oneidensis is able to produce H 2 S through both cysteine degradation and respiration of sulfur species (13)(14)(15). Under aerobic conditions, H 2 S produced through respiration is negligible, especially when the relevant sulfur species is not added (15). Thus, endogenous H 2 S results from the activity of the CSE homologues MdeA and SO1095, as well as from the 3MST homologue SseA, with MdeA accounting for Ͼ70% (15) (Fig.…”

“…To keep levels of H 2 S from both endogenous and exogenous sources in growing cultures relatively stable, cells for H 2 S-related physiological assays were grown under aerobic conditions on a shaker at 50 rpm at 30°C. H 2 S production in S. oneidensis was monitored by a lead acetate detection method and the methylene blue formation assay (3,15,22). Mutagenesis and genetic complementation.…”

“…Cysteine degradation via methionine ␥-lyase MdeA is the predominant source of endogenous H 2 S production, with other mechanisms via SO_1095 and SseA being of lesser importance (15). While MdeA and SO_1095 are homologous to P. aeruginosa cystathionine ␥-lyase (CSE), SseA is a homologue of 3-mercaptopyruvate sulfurtransferase (3MST) (3,15,17).…”

“…Owing to these properties, some species, the model species Shewanella oneidensis in particular, have been intensively studied. There is endogenous H 2 S generation in S. oneidensis (12), but not until recently was its enzymatic foundation determined (13)(14)(15). Through anaerobic respiration of inorganic sulfur compounds in the periplasm, including thiosulfate (S 2 O 3 2Ϫ ), sulfite (SO 3 2Ϫ ), tetrathionate (S 4 O 6 2Ϫ ), and elemental sulfur (S 0 ), S. oneidensis generates H 2 S with sulfite reductase SirACD, as well as thiosulfate and polysulfide reductase PsrABC (13,14,16).…”

“…Through anaerobic respiration of inorganic sulfur compounds in the periplasm, including thiosulfate (S 2 O 3 2Ϫ ), sulfite (SO 3 2Ϫ ), tetrathionate (S 4 O 6 2Ϫ ), and elemental sulfur (S 0 ), S. oneidensis generates H 2 S with sulfite reductase SirACD, as well as thiosulfate and polysulfide reductase PsrABC (13,14,16). Cysteine degradation via methionine ␥-lyase MdeA is the predominant source of endogenous H 2 S production, with other mechanisms via SO_1095 and SseA being of lesser importance (15). While MdeA and SO_1095 are homologous to P. aeruginosa cystathionine ␥-lyase (CSE), SseA is a homologue of 3-mercaptopyruvate sulfurtransferase (3MST) (3,15,17).…”