Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 52, Issue 17, Pages 10030-10039Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.8b01305
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Funding
- National Science Foundation [CHE-1308504]
- Undergraduate Research Grant Program
- E.I. DuPont de Nemours Co.
- Dow Chemical Company
- U.S. National Science Foundation [DMR-9304725]
- State of Illinois through the Department of Commerce
- Board of Higher Education [IBHE HECA NWU 96]
- Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource [NSF ECCS-1542205]
- MRSEC program at the Materials Research Center
- the International Institute for Nanotechnology (IIN) [NSF DMR-1121262]
- Keck Foundation
- State of Illinois, through the IIN
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We investigated the chemistry of Hg(II) during exposure of exponentially growing bacteria (Escherichia coli, Bacillus subtilis, and Geobacter sulfurreducens) to 50 nM, 500 nM, and 5 mu M total Hg(II) with and without added cysteine. With X-ray absorption spectroscopy, we provide direct evidence of the formation of cell-associated HgS for all tested bacteria. The addition of cysteine (100-1000 mu M) promotes HgS formation (>70% of total cell-associated Hg(II)) as a result of the biodegradation of added cysteine to sulfide. Cell-associated HgS species are also detected when cysteine is not added as a sulfide source. Two phases of HgS, cinnabar (alpha-HgS) and metacinnabar (beta-HgS), form depending on the total concentration of Hg(II) and sulfide in the exposure medium. However, alpha-HgS exclusively forms in assays that contain an excess of cysteine. Scanning transmission electron microscopy images reveal that nanoparticulate HgS(s) is primarily located at the cell surface/extracellular matrix of Gram-negative E. coli and G. sulfurreducens and in the cytoplasm/cell membrane of Gram-positive B. subtilis. Intracellular Hg(II) was detected even when the predominant cell-associated species was HgS. This study shows that HgS species can form from exogenous thiol-containing ligands and endogenous sulfide in Hg(II) biouptake assays under nondissimilatory sulfate reducing conditions, providing new considerations for the interpretation of Hg(II) biouptake results.
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