Depletion of proton motive force by nisin in Listeria monocytogenes cells

The basal proton motive force (PMF) levels and the influence of the bacteriocin nisin on the PMF were determined in Listeria monocytogenes Scott A. In the absence of nisin, the interconversion of the pH gradient and the membrane potential led to the maintenance of a fairly constant PMF at -160 mV over the external pH range 5.5 to 7.0. The addition of nisin at concentrations of greater than or equal to 5 microgram/ml completely dissipated PMF in cells at external pH values of 5.5 and 7.0. With 1 microgram of nisin per ml, pH gradient was completely dissipated but membrane potential decreased only slightly. The action of nisin on PMF in L. monocytogenes Scott A was both time and concentration dependent. Valinomycin depleted only membrane potential, whereas nigericin and carbonyl cyanide m-chloro-phenylhydrazone depleted only pH gradient, under conditions in which nisin depleted both. Four other L. monocytogenes strains had basal PMF parameters similar to those of strain Scott A. Nisin (2.5 microgram/ml) also completely dissipated PMF in these strains.