Multiple-pathway remediation of mercury contamination by a versatile selenite-reducing bacterium

Mercury contamination is a global concern because of its high toxicity, persistence, bioaccumulative nature, long distance transport and wide distribution in the environment. In this study, the efficiency and multiple-pathway remediation mechanisms of Hg2+ by a selenite reducing Escherichia coli was assessed. E. coli can reduce Hg2+ to Hg+ and Hg-0 and selenite to selenide at the same time. This makes amultiple-pathway mechanisms for removal of Hg2+ from water in addition to biosorption. It was found that when the original Hg2+ concentration was 40 mu g L-1, 93.2 +/- 2.8% of Hg2+ was removed from solution by E. coli. Of the total Hg removed, it was found that 3.3 +/- 0.1% was adsorbed to the bacterium, 2.0 +/- 0.5% was bioaccumulated, and 7.3 +/- 0.6% was volatilized into the ambient environment, and most (80.6 +/- 5.7%) Hg was removed as HgSe and HgCl precipitates and Hg-0. On one hand, selenite is reduced to selenide and the latter further reacts with Hg2+ to form HgSe precipitates. On the other hand Hg2+ is successively reduced to Hg+, which forms solid HgCl, and Hg-0. This is the report on bacterially transformation of Hg2+ to HgSe, HgCl and Hg-0 via multiple pathways. It is suggested that E. coli or other selenite reducing microorganisms are promising candidates for mercury bioremediation of contaminated wastewaters, as well as simultaneous removal of Hg2+ and selenite. (C) 2017 Elsevier B.V. All rights reserved.