Abstract
The bacterial uptake of mercury(II), Hg(II), is believed to be energy-dependent and is enhanced by cysteine in diverse species of bacteria under aerobic and anaerobic conditions. To gain insight into this Hg(II) biouptake pathway, we have employed X-ray absorption spectroscopy (XAS) to investigate the relationship between exogenous cysteine, cellular metabolism, cellular localization, and Hg(II) coordination in aerobically respiring Escherichia coli (E. coli). We show that cells harvested in exponential growth phase consistently display mixtures of 2-fold and 4-fold Hg(II) coordination to sulfur (Hg-S2 and Hg-S4), with added cysteine enhancing Hg-S4 formation. In contrast, cells in stationary growth phase or cells treated with a protonophore causing a decrease in cellular ATP predominantly contain Hg-S2, regardless of cysteine addition. Our XAS results favor metacinnabar (β-HgS) as the Hg-S4 species, which we show is associated with both the cell envelope and cytoplasm. Additionally, we observe that added cysteine abiotically oxidizes to cystine and exponentially growing E. coli degrade high cysteine concentrations (100-1000 μM) into sulfide. Thermodynamic calculations confirm that cysteine-induced sulfide biosynthesis can promote the formation of dissolved and particulate Hg(II)-sulfide species. This report reveals new complexities arising in Hg(II) bioassays with cysteine and emphasizes the need for considering changes in chemical speciation as well as growth stage.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4642-4651 |
| Number of pages | 10 |
| Journal | Environmental Science and Technology |
| Volume | 51 |
| Issue number | 8 |
| DOIs | |
| State | Published - Apr 18 2017 |
Funding
We would like to thank Dr. Qing Ma for his beamline assistance at the APS as well as Drs. Kevin Schwartzenberg and Marco Alsina for technical assistance. Dr. Patrice Catty's assistance with the genomic analysis of E. coli ATCC 25922 is greatly appreciated. Additionally, we are grateful for the suggestions from the anonymous reviewers to improve this manuscript. Portions of this work were performed at the DND-CAT Synchrotron Research Centre 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. This work is supported by the National Science Foundation under grant CHE-1308504 and made use of the J.B. Cohen X-ray Diffraction Facility supported by the MRSEC program of the National Science Foundation (DMR-1121262) at the Materials Research Center of Northwestern University.
ASJC Scopus subject areas
- General Chemistry
- Environmental Chemistry