Volatilization and recovery of mercury from mercury-polluted soils and wastewaters using mercury-resistant Acidithiobacillus ferrooxidans strains SUG 2-2 and MON-1.

Iron-oxidizing bacterium, Acidithiobacillus ferrooxidans, is one of the most important bacteria for the bioleaching of copper and gold ores. In order to use the mercury reducing activity of A. ferrooxidans for the bioremediation of mercury, mercury-resistant A. ferrooxidans strains SUG 2-2 and MON-1 were screened among 150 strains of iron-oxidizing bacteria isolated from natural environments. It was found that strains SUG 2-2 and MON-1 have a novel ferrous iron-dependent mercury volatilization activity as well as an NADPH-dependent mercury reductase activity. Strain MON-1 has an organomercurial lyase-like activity and grew most rapidly in an iron medium with 0.1 microM p-chloromercuribenzoic acid among 11 A. ferrooxidans strains tested. Nearly 100% of the total mercury in mercury-polluted soil or mercury wastewater was volatilized and recovered by incubating SUG 2-2 or MON-1 cells in 20 ml of an acidified water (pH 2.5) with ferrous iron, suggesting that these mercury-resistant strains can be used for the bioremediation of inorganic and organic mercurial compounds. We show for the first time that MON-1 cells immobilized in polyvinyl alcohol (PVA) resins could efficiently volatilize mercury from 2 L of a synthetic mercury-polluted wastewater (pH 2.5) containing 40 microM Hg(2+) and ferrous iron. The MON-1-immobilized PVA resins were used repeatedly.