High methylation potential of mercury complexed with mixed thiolate ligands by Geobacter sulfurreducens PCA

Xujun Liang, Alexander Johs, Macon J. Abernathy, Jiating Zhao, Hongxia Du, Peijia Ku, Lijie Zhang, Nali Zhu, Xiangping Yin, Scott Brooks, Linduo Zhao, Ritimukta Sarangi, Eric M. Pierce, Baohua Gu

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Some thiols, such as cysteine (CYS) at moderate concentrations (10–500 µM), can enhance methylmercury (MeHg) formation by Geobacter sulfurreducens PCA, whereas others such as dithiol 2,3-dimercaptopropanesulfonate (DMPS) and 2,3-dimercaptosuccinic acid (DMSA) abolish mercury [Hg(II)] methylation. Little is known, however, about whether Hg(II) methylation could be enhanced or inhibited by the presence of mixed thiol ligands at low concentrations observed in the environment. Surprisingly we found that mixing CYS (1 µM) with DMPS (0.025–0.5 µM) or DMSA (0.025–1 µM) substantially increased MeHg production by 1.5–3.5-fold, compared to the no-thiol control, whereas complexation with a single DMPS, or DMSA, or CYS (1 µM) strongly inhibited Hg(II) methylation. Pre-equilibration between Hg(II) and thiols before the addition of cells was necessary to observe enhanced methylation. Spectroscopic analyses indicated the formation of mixed or heteroleptic coordinated Hg(II)-S3/S4 complexes, which likely facilitated exchange of Hg(II) with cells and its uptake and internal transfer to the HgcAB proteins required for methylation. These results suggest that the effects of thiols on Hg(II) methylation were more complex than previously thought (using a single thiol) and thus underscore the importance of understanding how mixed thiols and their interactions with Hg(II) may ultimately influence MeHg production in the natural environment.

Original languageEnglish (US)
Pages (from-to)74-83
Number of pages10
JournalGeochimica et Cosmochimica Acta
StatePublished - Feb 1 2023
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology


  • Coordination
  • Dithiols
  • Hg-thiol complexes
  • Methylmercury
  • Microbial methylation


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