Cell-free mercury volatilization activity from three marine caulobacter strains

Three mercury-resistant marine Caulobacter strains showed an inducible mercury volatilization activity. Cell-free mercury volatilization (mercuric reductase) from these three marine Caulobacter strains was characterized and compared with enzyme activities determined by plasmids of Escherichia coli and Staphylococcus aureus. The temperature sensitivity of the Caulobacter mercuric reductase was greater than that of mercuric reductase from other gram-negative sources. Cell-free enzyme activity required NADH or NADPH, with NADPH functioning much better at lower concentrations than NADH. The Km for the Caulobacter enzyme was 4 microM Hg2+. Ag+ was a competitive inhibitor of Caulobacter mercuric reductase (Ki = 0.2 microM Ag+), as with previously studied enzymes. Arsenite was a noncompetitive inhibitor of the Caulobacter enzyme with a Ki of 75 microM AsO2-.