TY - JOUR
T1 - Spectroscopic and Microscopic Evidence of Biomediated HgS Species Formation from Hg(II)-Cysteine Complexes
T2 - Implications for Hg(II) Bioavailability
AU - Thomas, Sara A.
AU - Rodby, Kara E.
AU - Roth, Eric W.
AU - Wu, Jinsong
AU - Gaillard, Jean François
N1 - Funding Information:
We are grateful to Qing Ma for his beamline assistance at the APS. We thank Dr. Isabelle Michaud-Soret for helpful discussions regarding this study. This work is supported by the National Science Foundation under grant CHE-1308504 and a grant to K.E.R. from the Undergraduate Research Grant Program administered by Northwestern University’s Office of the Provost. Portions of this work were performed at the DND-CAT Synchrotron Research Center located at Sector 5 of the APS. DND-CAT is supported by the E.I. DuPont de Nemours & Co., The Dow Chemical Company, the U.S. National Science Foundation through Grant DMR-9304725, and the State of Illinois through the Department of Commerce and the Board of Higher Education Grant IBHE HECA NWU 96. The STEM and TEM work made use of the BioCryo and EPIC facility of Northwestern University’s NUANCE Center, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); the Keck Foundation; and the State of Illinois, through the IIN. Finally, we thank four anonymous reviewers for their helpful suggestions.
Publisher Copyright:
© 2018 American Chemical Society.
PY - 2018/9/4
Y1 - 2018/9/4
N2 - 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 μM 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 μM) 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 (α-HgS) and metacinnabar (β-HgS), form depending on the total concentration of Hg(II) and sulfide in the exposure medium. However, α-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.
AB - 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 μM 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 μM) 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 (α-HgS) and metacinnabar (β-HgS), form depending on the total concentration of Hg(II) and sulfide in the exposure medium. However, α-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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U2 - 10.1021/acs.est.8b01305
DO - 10.1021/acs.est.8b01305
M3 - Article
C2 - 30078312
AN - SCOPUS:85052303072
SN - 0013-936X
VL - 52
SP - 10030
EP - 10039
JO - Environmental Science and Technology
JF - Environmental Science and Technology
IS - 17
ER -