The role of cysteine and sulfide in the interplay between microbial Hg(ii) uptake and sulfur metabolism.
Sara A ThomasPatrice CattyJean-Louis HazemannIsabelle Michaud-SoretJean-François GaillardPublished in: Metallomics : integrated biometal science (2020)
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.
Keyphrases
- fluorescent probe
- living cells
- aqueous solution
- wild type
- escherichia coli
- high resolution
- cell therapy
- density functional theory
- computed tomography
- magnetic resonance
- gene expression
- stem cells
- microbial community
- blood pressure
- single molecule
- cystic fibrosis
- mesenchymal stem cells
- mass spectrometry
- high speed
- genetic diversity
- molecular dynamics simulations