Drug extrusion in Corynebacterium glutamicum

We selected a mutant of Corynebacterium glutamicum, EBR, which can grow in a medium containing cytotoxic ethidium bromide (EtBr) at a high concentration of 100 mu M. The resistance to EtBr in the mutant was reversed by 2 mu M reserpine, a potent inhibitor of mammalian p-glycoprotein and bacterial multidrug resistance (MDR) transporter, whereas reserpine alone had a minimal effect on cell growth, The mutant showed a much higher efflux rate of EtBr than mild-type cells, and the efflux was completely inhibited by 2 mu M reserpine, In addition to reserpine, structurally unrelated chemicals such as quinidine, trifluorperazine, tetraphenylarsonium chloride, chlorpromazine and quinine inhibit the EtBr efflux, revealing that the putative efflux system(s) can recognize a variety of chemicals. The efflux activity was correlated with the membrane potential but not the intracellular ATP contents. We, therefore, concluded that the EtBr resistance may be involved by proton-motive-force driven multidrug efflux system(s).