An Expanded Substrate Spectrum of Sulfide:Quinone Oxidoreductase Found in Pollutant Degrading Bacteria

Abstract

Sulfide:quinone oxidoreductase (Sqr) catalyzes the initial procedure on sulfide transformation, alongside sulfide (H2S, S2‐) oxidization coupled with coenzyme Q (CoQ) reducing and reactive sulfur species (RSS) production. Here, we assessed the reactivity of propanethiol (PT) as an alternative substrate for Sqr to maintain intracellular homeostasis in strain S‐1 capable of degrading emerging sulfur‐containing pollutants. We deleted a gene encoding Sqr, and serial transcriptional difference induced by RSS dynamics was therefore revealed. Next, the reaction properties of two Sqr homologs from strains JMP134 and S‐1 were comparatively characterized, respectively. As a result, an additional role of Sqr in yielding RSS from PT was found in reaction mixture prepared by cell‐free extracts or purified enzymes. Interestingly, the transformation velocity of PT by Sqr was slower than that of sulfides. From this scenario, it was a rate‐determining step that PT as a nucleophilic compound can be added into Sqr cysteine to form disulfide bond and likely serve nonoptimal sulfur recipient. In addition, the role of persulfidation driven by RSS in combating oxidative and sulfur stresses required to be further clarified. Nevertheless, this promiscuity of Sqr‐binding organosulfur compounds and its catalytic modulation underscored that expanded substrates might benefit sulfide homeostasis in thiol‐degrading bacteria.