Lavoie N C, Poulain A J
Department of Biology, Faculty of Sciences, University of Ottawa, Ottawa, Canada.
Access Microbiol. 2025 Jan 28;7(1). doi: 10.1099/acmi.0.000932.v3. eCollection 2025.
Redox reactions play a critical role in determining the availability of mercury species, Hg and Hg, to anaerobic microbes responsible for methylating inorganic mercury into toxic monomethylmercury. Some anaerobes also contribute to Hg cycling in methylation hotspots by reducing Hg to its gaseous elemental form, Hg. However, their contributions remain poorly quantified due to limited mechanistic insights and the absence of genetic targets. In this study, we investigated the mechanisms of anaerobic Hg reduction in the versatile anoxygenic photoheterotroph and fermenter Ice1. Given Hg strong electrophilic affinity for thiol groups, we hypothesized that cellular thiols are key interaction sites mediating Hg reduction. Exposure of to the thiol-alkylating agent -ethylmaleimide (NEM), which irreversibly binds thiols, resulted in a concentration-dependent inhibition of Hg production during both photoheterotrophy and fermentation. Hg partitioning assays with cells revealed no significant differences in Hg-cell partitioning in the presence or absence of NEM, suggesting that Hg reduction is dependent on intracellular thiol interactions. These findings highlight the importance of thiol-mediated pathways in Heliobacterial Hg reduction. Although the exact cellular components remain unidentified, we discuss potential thiol-containing coupling sites that warrant further investigation.
氧化还原反应在决定汞物种（Hg和Hg）对负责将无机汞甲基化为有毒单甲基汞的厌氧微生物的可用性方面起着关键作用。一些厌氧菌还通过将Hg还原为气态元素形式Hg，在甲基化热点区域的汞循环中发挥作用。然而，由于机理认识有限和缺乏遗传靶点，它们的贡献仍难以量化。在本研究中，我们研究了多功能无氧光合异养菌和发酵菌Ice1中厌氧汞还原的机制。鉴于Hg对硫醇基团具有很强的亲电亲和力，我们假设细胞内硫醇是介导汞还原的关键相互作用位点。将Ice1暴露于硫醇烷基化剂N - 乙基马来酰亚胺（NEM），其与硫醇不可逆结合，在光合异养和发酵过程中均导致汞产生的浓度依赖性抑制。对Ice1细胞进行的汞分配分析表明，在存在或不存在NEM的情况下，汞 - 细胞分配没有显著差异，这表明汞还原依赖于细胞内硫醇相互作用。这些发现突出了硫醇介导的途径在嗜盐杆菌汞还原中的重要性。尽管确切的细胞成分仍未确定，但我们讨论了值得进一步研究的潜在含硫醇偶联位点。
