Interaction of nisin with planar lipid bilayers monitored by fluorescence recovery after photobleaching

Nisin, a prominent member of the lantibiotic family of antimicrobial agents, has wide application as a food preservative despite poor understanding of its mode of action. Fluorescence recovery after photobleaching has been used with planar lipid bilayers as a model membrane system to examine how nisin might interact with the surface of bacterial cells. Nisin associates with planar lipid bilayers in the absence of an applied membrane potential causing an array of effects consistent with adsorption of nisin onto the membrane surface which involves inhibition of the lateral diffusion and fluorescence of the lipid probe N-(7--1,2,3-benzoxadiazol-4-yl) phosphatidylethanolamine (NBD-PE) and a reduction of the capacitance of the bilayer. Nisin adsorption is dependent on phospholipid composition. In the presence of dioleoylphosphatidylcholine (PC): cardiolipin (CL) 4:1, the rate of lateral mobility of phospholipid is reduced to 61% of the control level which decreases to a value of 46% when CL is replaced by 1-palmitoyl-2-oleoylphosphatidylserine (PS). These effects on bilayer parameters are transient, and with time the values return to near original levels. High electrical conductivity is observed on application of a voltage ramp suggesting that insertion into the membrane follows surface association. Results have been interpreted in terms of a model in which nisin initially binds to the surface of the membrane causing a modulation of bilayer properties.