LACK OF INVOLVEMENT OF MERT AND MERP IN METHYLMERCURY TRANSPORT IN MERCURY RESISTANT PSEUDOMONAS K-62

To clarify whether the merT and merP genes play a role in the transport of methylmercury, we constructed a deletion plasmid, pMRD141 which lacked the genes conferring the organomercurial lyase and the mercuric reductase from plasmid, pMRA17 containing the entire broad-spectrum mercury resistance determinants of the 26 kb-plasmid from Pseudomonas K-62. Plasmid, pMRD141 showed hypersensitivity to Hg2+ but still expressed a normal sensitivity to methylmercury. The mercury-induced hypersensitive cells carrying pMRD141 took up appreciably more Hg-203(2+) than the induced resistant cells with pMRA17 and the sensitive cells with cloning vector, Bluescript II SK(+) but no difference in the uptake of (CH3Hg+)-Hg-203 among these three strains was found. These results suggested that the merT and merP are only involved in the Hg2+ transport but do not participate in the transport of methylmercury.