Feedback inhibition derived from hydrogen sulfide in microbial sulfidogenic process via elemental sulfur...

Elemental sulfur disproportionation (S⁰Disp), a key sulfidogenic process, has not only been known to play significant roles in biogeochemical sulfur cycles but has also received increasing attention in various wastewater treatment systems. For a sulfidogenic process, understanding the feedback inhibition (FBI) derived from the sulfide it produces is essential and fundamental, while this issue has yet to be systematically studied within the context of S⁰Disp. In this study, the FBI for S⁰Disp was investigated in Desulfocapsa-enriched mixed cultures. H₂S was identified as the form of sulfide to bring about the FBI directly, which has a half-maximal inhibitory concentration (IC₅₀-H₂S) and an almost complete inhibitory concentration (IC_threshold-H₂S) at 22 mg-S/L and 40 mg-S/L, respectively. The IC_threshold-H₂S was also found to be a critical concentration in governing the FBI from reversible to irreversible. Furthermore, based on the metatranscriptomic analysis, the possible metabolic pathways of S⁰Disp were proposed, implying the mechanism of H₂S-derived FBI may be involved in the deactivation of heme-functional enzymes (e.g., dsrAB, qmoABC, and sox) and the substrate (persulfide) deficiency of the hdrABC-catalyzed reaction. The findings of this study will not only help to better understand the S⁰Disp-involved natural water systems but can also guide the optimization of the S⁰Disp-related wastewater treatment systems.