
Full text loading...
Metal Resistance Loci of Bacterial Plasmids, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555817572/9781555813291_Chap11-1.gif /docserver/preview/fulltext/10.1128/9781555817572/9781555813291_Chap11-2.gifAbstract:
This chapter provides an introduction to metallobiology, brief descriptions of the well-studied plasmidcoded metal resistances, and a short survey of the genetic and biochemical connections between metals and antibiotic resistances. Many genes in bacterial plasmid-borne metal resistance systems are homologous to those of the chromosomal homeostasis systems. Cobalt, nickel, and zinc are all essential metals, and all but zinc are redox active. Lead and cadmium have no beneficial biological functions and are both quite toxic. Operons conferring single and multiple resistances to various subsets of these four transition metals and the main group heavy metal, lead, are based on several distinct types of efflux pumps. In R. metallidurens there are three metal resistance loci on pMOL28: a transposon conferring resistance to mercury, merTPADE, and two nontransposable loci conferring resistance to chromate and to cobalt and nickel. Although heavy metal resistances in bacteria first appeared to be largely plasmid encoded, genome sequencing has revealed that homologs of transition metal resistance genes and their regulators abound in all prokaryotic chromosomes, most likely for managing the cell’s use of their beneficial and essential metal relatives. It is a known fact that bacteria isolated from metal-impacted environments typically carry several metal resistances on large conjugative plasmids, suggesting that this genetic arrangement has selective advantage beyond that afforded by expression of related chromosomal loci.