Mode of Action of Nisin Z against Listeria monocytogenes Scott A Grown at High and Low Temperatures

Nisin Z, a natural nisin variant, was recently isolated from Lactococcus lactis subspecies lactis NIZO 22186. The gene for this lantibiotic, designated nisZ, has been cloned, and its nucleotide sequence was found to be identical to that of the precursor nisin gene with the exception of a single mutation resulting in the substitution of Asn-27 for His-27 in the mature polypeptide (J. W. M. Mulders, I. J. Boerrigter, H. S. Rollema, R. J. Siezen, and W. M. de Vos, Eur. J. Biochem. 201:581-584, 1991). A K⁺ electrode was used to investigate the effect of various environmental parameters on the action of nisin Z against Listeria monocytogenes. Addition of nisin Z resulted in immediate loss of cell K⁺, depolarization of the cytoplasmic membrane, inhibition of respiratory activity, and hydrolysis and partial efflux of cellular ATP. The action of nisin Z was optimal at pH 6.0 and was significantly reduced by di- and trivalent cations. The lanthanide gadolinium (Gd³⁺) was an efficient inhibitor and prevented nisin Z activity completely at a concentration of 0.2 mM. Nisin Z-induced loss of cell K⁺ was reduced at low temperatures, presumably as a result of the increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30°C, the action of nisin Z was prevented below 7°C, whereas in cells grown at 4°C nisin Z was able to induce K⁺ leakage at this low temperature.