The role of cysteine and sulfide in the interplay between microbial Hg(ii) uptake and sulfur metabolism. Issue 7 (30th May 2019)

• Record Type: Journal Article
• Authors: Thomas, Sara A.; Catty, Patrice; Hazemann, Jean-Louis; Michaud-Soret, Isabelle; Gaillard, Jean-François
• Is Part Of: Metallomics. Volume 11:Issue 7(2019)
• Page Start: 1219
• Page End: 1229
• Publication Date: 2019-05-30
• Subjects: Metals -- Physiological effect -- Periodicals; 572.51
• DOI: 10.1039/c9mt00077a
• Languages: English
• ISSNs: 1756-5901

Abstract

Abstract : Mercury uptake by E. coli in the presence of excess cysteine is facilitated by the biodegradation of cysteine to sulfide and the formation of mercury sulfide species. The deletion of a key cysteine desulfhydrase gene ( decR ) limits the uptake of mercury in the presence of excess cysteine. 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.