Plasmid-controlled mercury biotransformation by Clostridium cochlearium T-2

A strain of Clostridium cochlearium having methylmercury-decomposing ability was isolated. The ability was cured by the treatment with acridine dye and recovered by the conjugation of the cured strain with the parent strain. The cured strain then showed the activity to methylate mercuric ion as previously reported (M. Yamada and K. Tonomura, J. Ferment. Technol. 50:159-166, 1971). These results and the agarose gel electrophoretic pattern of the deoxyribonucleic acids from the lysates indicate a possible role of plasmids in controlling the mercury biotransformation of the two opposite directions in a single bacterial strain: methylation in the absence of the plasmid and demethylation in the presence of it. A possible mechanism for mercury resistance involving hydrogen sulfide is discussed.