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 Hg(2+) by a selenite reducing Escherichia coli was assessed. E. coli can reduce Hg(2+) to Hg(+) and Hg(0) and selenite to selenide at the same time. This makes a multiple-pathway mechanisms for removal of Hg(2+) from water in addition to biosorption. It was found that when the original Hg(2+) concentration was 40μgL(-1), 93.2±2.8% of Hg(2+) 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 Hg(2+) to form HgSe precipitates. On the other hand Hg(2+) is successively reduced to Hg(+), which forms solid HgCl, and Hg(0). This is the report on bacterially transformation of Hg(2+) 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 Hg(2+) and selenite.