Abstract
Biogenic thiols, such as cysteine, have been used to control the speciation of Hg(ii) in bacterial exposure experiments. However, the extracellular biodegradation of excess cysteine leads to the formation of Hg(ii)-sulfide species, convoluting the interpretation of Hg(ii) uptake results. Herein, we test the hypothesis that Hg(ii)-sulfide species formation is a critical step during bacterial Hg(ii) uptake in the presence of excess cysteine. An Escherichia coli (E. coli) wild-type and mutant strain lacking the decR gene that regulates cysteine degradation to sulfide were exposed to 50 and 500 nM Hg with 0 to 2 mM cysteine. The decR mutant released ∼4 times less sulfide from cysteine degradation compared to the wild-type for all tested cysteine concentrations during a 3 hour exposure period. We show with thermodynamic calculations that the predicted concentration of Hg(ii)-cysteine species remaining in the exposure medium (as opposed to forming HgS(s)) is a good proxy for the measured concentration of dissolved Hg(ii) (i.e., not cell-bound). Likewise, the measured cell-bound Hg(ii) correlates with thermodynamic calculations for HgS(s) formation in the presence of cysteine. High resolution X-ray absorption near edge structure (HR-XANES) spectra confirm the existence of cell-associated HgS(s) at 500 nM total Hg and suggest the formation of Hg-S clusters at 50 nM total Hg. Our results indicate that a speciation change to Hg(ii)-sulfide controls Hg(ii) cell-association in the presence of excess cysteine.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1219-1229 |
| Number of pages | 11 |
| Journal | Metallomics |
| Volume | 11 |
| Issue number | 7 |
| DOIs | |
| State | Published - Jul 2019 |
Funding
This work is supported by the National Science Foundation under grant CHE-1308504 and is based upon research supported by the Chateaubriand Fellowship of the Office for Science & Technology of the Embassy of France in the United States. We thank Dr Mireille Chevallet and Dr Xavier Maréchal for assistance with the bacterial cultures. The experiments were performed on beamlines BM30B – FAME – and BM16 – UHD-FAME – at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The FAME-UHD project is financially supported by the French ‘‘grand emprunt’’ EquipEx (EcoX, ANR-10-EQPX-27-01), the CEA-CNRS CRG consortium and the INSU CNRS institute. We are grateful for the beamline assistance of Dr Olivier Proux and Dr Mauro Rovezzi at the ESRF. The 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. We thank Dr Jinsong Wu for his assistance with the STEM and TEM imaging.
ASJC Scopus subject areas
- General Medicine