"Most toxic metals and radionuclides can be naturally rendered insoluble-immobile by bacterial reduction, which may be exploited for bioremediation purposes at waste repository sites. Some bacteria (e.g. iron or sulphate respirers) are receiving intense attention as their envelope-located electron transport chain can carry out such reductions. However, this process is subject to inhibition by nitrate and oxygen, usually present at waste sites. It also involves 1 e- transfer reactions generating reactive oxygen species which poison the cells and hamper remediation, and the reduced species are released outside the cells, where re-oxidation may occur rapidly. An alternative ""safe"" bacterial pathway for reduction of metals-radionuclides has been discovered recently at the host laboratory (Dr. AC Matin). It involves proteins from the widely distributed ChrR enzyme family, performing 2 e- (4 e-) transfer processes strongly reducing oxidative stress, and leads to sequestering of reduced species. Strengthening this pathway should lessen metal toxicity and increase bioremediation capabilities. The objectives of this multidisciplinary project are (1) to assess this reduction process in bioreactors simulating waste sites conditions, using an engineered strain producing a highly improved ChrR, by analysing the oxidation state and distribution of reduced products; (2) as minor mutations of ChrR led to its increased efficiency, to test the hypothesis that improved ChrR activity is naturally present at US waste sites, where bacteria have been exposed to metals for over 50 years; (3) to test if the intra-cellular reduced products are indeed less amenable to re-oxidation than extra-cellular ones; and (4) to use the skills gained for the identification of new cytoplasmic enzymes with safe metal reduction mechanisms in uranyl-rich soils from Bessines (France), where bacterial communities with effective means of safe enzymatic reduction of uranyl are likely to have naturally evolved."
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