In vitro pore-forming activity of the lantibiotic nisin. Role of protonmotive force and lipid composition.

Nisin is a lantibiotic produced by some strains of Lactococcus lactis subsp. lactis. The target for nisin action is the cytoplasmic membrane of Gram-positive bacteria. Nisin dissipates the membrane potential (delta psi) and induces efflux of low-molecular-mass compounds. Evidence has been presented that a delta psi is needed for nisin action. The in vitro action of nisin was studied on liposomes loaded with the fluorophore carboxyfluorescein. Nisin-induced efflux of carboxyfluorescein was observed in the absence of a delta psi from liposomes composed of Escherichia coli lipids or dioleoylglycerophosphocholine (Ole2GroPCho) at low nisin/lipid ratios. The initial rate of carboxyfluorescein efflux is dependent on the nisin/lipid ratio and saturates at high ratios. Both delta psi (inside negative) and delta pH (inside alkaline) enhance the action of nisin, while nisin is more potent at acidic external pH values. Efficient carboxyfluorescein efflux is observed with the zwitterionic phospholipid Ole2GroPCho or mixtures of Ole2GroPCho with dioleoylglycerophosphoethanolamine and neutral glycolipids, while anionic phospholipids are strongly inhibitory. It is concluded that a delta psi is not essential, but that the total protonmotive force stimulates the action of nisin.