[Comparative study of plasmid resistance to mercury of 2 bacterial strains of animal origin]

Bacterial resistance to mercury has been studied in two different strains from animal origin, Salmonella typhimurium 9205 and Escherichia coli 467. These two strains are resistant to mercuric chloride but sensitive to phenylmercury, and thus belong to the group of bacteria that possess a "narrow" spectrum resistance. The presence of plasmids within the cells has been demonstrated through conjugation experiments and direct detection of extrachromosomal DNA in transconjugants. These plasmids, termed p9205-1 and p467-30, differ from each other by both their size (100 and 50 Kbp, respectively) and structure, as shown by the restriction patterns arising from digestion by nucleases BamHI, HindIII, PstI and EcoRI. Each plasmid has been treated with enzyme SalI to yield DNA fragments that have been cloned into pBR322. Two recombinant plasmids, p9205-1/Sal and p467-30/Sal, have thus been constructed, each of them harboring a 2 Kbp fragment that appears to contain the merA gene coding for mercuric reductase. From the analysis of the restriction maps of these recombinant plasmids as well as the functional behaviour of the bacteria that they are able to transform, it can be concluded that they are identical.