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

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 (ICthreshold-H2S) at 22 mg-S/L and 40 mg-S/L, respectively. The ICthreshold-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.