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Abstract Title: Coupling Fluorescent Probes to Characterize S-Containing Compounds in a Mercury Methylating SRB Bacteria
Presenter Name: IKRAM BAKOUIR
Company/Institution: IPREM-UMR
Session: Special Session - Meta-omic and geochemical approaches to linking microbial activity to biogeochemical mercury cycling

Abstract Information :

Microbial methylation/demethylation of mercury is known to be governed by S-containing compounds such as thiols and sulfides. However, a clear understanding of the interaction of these compounds with Hg species is still limited, especially because analytical methods used to characterize these S-containing compounds in bacteria assay are limited due to their low concentrations, propensity to oxidation, and matrix interferences. Here, we present two fluorescence spectroscopy-based methods using monobromo(trimethylammonio)bimane (qBBr) probe for estimating total thiol concentrations (extracellular and on bacteria cells) and à, ?-unsaturated ethanoylcoumarin fluorophore (DHC) for the quantification of sulfide. The two procedures have been optimized in order to decrease the detection limit in the nM range. Potential interferences have been evaluated both with organic and inorganic compounds presents in the matrix. The optimized methods are found highly sensitive with detection limits of 100 nM and 20 nM for thiols and sulfides, respectively. They also exhibit high selectivity for the detection of either thiols or sulfides against others matrix compounds. Finally, the two methods have been successfully applied to the characterization of S-containing compounds in a culture of Pseudodesulfovibrio hydrargyri strain BerOc1, a methylating SRB bacterium exposed to 0.1mM of cysteine. We also determine the distribution of thiols between extracellular and adsorbed on the cells during the bacterial growth. The time series until the end of the BerOc1 growth have shown the biodegradation of cysteine and the biosynthesis of sulfide, as well as an increase in the thiol concentration on the growing BerOc1cells.

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