A PLASMID-ENCODED ARSENITE PUMP PRODUCES ARSENITE RESISTANCE IN ESCHERICHIA-COLI

The arsenate resistance operon of R factor R773, a conjugative resistance plasmid, has 2 functional regions, a promoter-proximal region encoding resistance to arsenite and antimonate, and a promoter-distal one encoding arsenate resistance. Cells bearing arsenite resistance plasmids exhibited reduced accumulation of 74AsO2-. When resistant cells were depleted of endogenous energy reserves and then loaded with 74AsO2-, active extrusion of the ion was observed when an energy source was supplied. Intracellular ATP was required for extrusion, but a proton motive force was neither necessary nor sufficient. An arsenite-sensitive mutant was unable to extrude arsenite, while an arsenate-sensitive mutant had nomral arsenite transport. Evidently, the action of a plasmid-encoded primary arsenite efflux pump is the mechanism of arsenite resistance.