Plasmid-encoded mercuric reductase in Mycobacterium scrofulaceum.

A Chesapeake Bay water isolate of Mycobacterium scrofulaceum containing a 115-megadalton plasmid (pVT1) grew in the presence of 100 microM HgCl2 and converted soluble 203Hg2+ to volatile mercury at a rate of 50 pmol/10(8) cells per min. Cell extracts contained a soluble mercuric reductase whose activity was not dependent on exogenously supplied thiol compounds. The enzyme displayed nearly identical activity when either NADH or NADPH served as the electron donor. A spontaneously cured derivative lacking pVT1 failed to grow in the presence of 100 microM HgCl2 and possessed no detectable mercuric reductase activity.