Energetics of tetracycline efflux system encoded by Tn10 in Escherichia coli

Tritiated tetracycline was actively accumulated in inverted membrane vesicles prepared from Escherichia coli W3104rif, which has a transposon, Tn10, on the plasmid, R388, by means of a protonmotive force when NADH was added as an energy source. The tetracycline accumulation was reduced to about one-half the full value on the addition of a cation/proton-exchange ionophore, nigericin. In contrast, remarkable stimulation of the tetracycline accumulation was observed with a K+-specific ionophore, valinomycin. The accumulation of [3H]tetracycline could also be driven by an artificially imposed interior-acidic pH gradient (delta pH), but not, however, by an artificially imposed interior-positive membrane potential (delta psi). These results strongly indicate that the plasmid-encoded tetracycline transport was mainly due to an electrically neutral proton/tetracycline antiport system.