Skyllberg, Ulf
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
Abstract
Mercury (Hg) is a global environmental concern due to its microbial conversion to methylmercury (MeHg), a potent neurotoxin that bioaccumulates in food webs and poses risks to ecosystems and human health. Thiol functional groups (RSH) play an important role in controlling Hg(II) speciation and bio-uptake in methylating bacteria, yet the spatial distribution and density of these thiols within cells remain largely unknown. We isolated subcellular fractions of the Hg methylating bacterium Geobacter sulfurreducens in the exponential growth phase, and used Hg LIII-edge EXAFS (Extended X-ray Absorption Fine Structure) to quantify thiols in the extracellular medium, inner and outer membranes, periplasm and cytoplasm. The whole-cell thiol content was determined to be 1.3 & times; 10-10 mu mol cell-1. The inner membrane contributed 7.1 & times; 10-11 (53%), the outer membrane 1.2 & times; 10-11 (9%), the periplasm 3.6 & times; 10-11 (27%) and the cytoplasm 1.5 & times; 10-11 mu mol cell-1 (11%). The extracellular fraction contributed an additional 5.7 & times; 10-11 mu mol cell-1, corresponding to 30% of the thiols of the cell culture. Local thiol density (thiols normalized to TOC in individual compartment, RSH/TOC, mu mol g-1 C) was 36, 450, 140, 600 and 29 mu mol g-1 C in the cytoplasm, inner membrane, periplasm, outer membrane and extracellular fractions, respectively. EXAFS analyses demonstrate Hg-thiolate coordination across all compartments, with Hg-O/N bonding and elemental Hg0 formed at higher Hg loadings. In the periplasm, Hg-disulfide and traces of beta-HgS were detected. The high thiol density at the membranes, relative to other compartments, may imply they have an important role in the retention and internalization of Hg(II). Periplasmic thiols may modulate Hg(II) transfer between membranes, and cytoplasmic thiols may regulate the intracellular availability of Hg(II) for methylation. This work provides the first compartment-resolved quantification of thiol abundances and densities in a model Hg-methylating bacterium at subcellular level, offering a mechanistic framework for understanding the speciation, bioavailability, and subcellular transformation of Hg(II) with relevance for other soft metals (e.g., Cd, Pb, Zn, Ag, and Cu).
Keywords
cellular thiols; mercury biogeochemistry; speciation and bioavailability; synchrotron X-ray absorption spectroscopy; uptake and methylation
Published in
Frontiers in Microbiology
2026, volume: 16, article number: 1728775
Publisher: FRONTIERS MEDIA SA
SLU Authors
Song, Yu
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
- University of Chinese Academy of Sciences
- Department of Forest Ecology and Management, Swedish University of Agricultural Sciences
UKÄ Subject classification
Analytical Chemistry
Environmental Sciences
Publication identifier
- DOI: https://doi.org/10.3389/fmicb.2025.1728775
Permanent link to this page (URI)
https://res.slu.se/id/publ/146412