MEMBRANE-ASSOCIATED PROTEINS ENCODED BY THE NISIN GENE-CLUSTER MAY FUNCTION AS A RECEPTOR FOR THE LANTIBIOTIC CARNOCIN UI49

Carnocin U149, a lantibiotic produced by Carnobacterium piscicola show s bactericidal activity against many lactic acid bacteria. This paper describes the results of a study on the mode of action of carnocin U14 9. It has previously been observed that nisin-producing Lactococcus la ctis subsp. lactis strains are at least 10-fold more sensitive to carn ocin U149 relative to other lactic acid bacteria. Addition of carnocin U149 to cells of L. lactis subsp. lactis NZ9700 resulted in a dissipa tion of the membrane potential and a rapid hydrolysis of internal ATP. These results suggest that carnocin U149 may act at the cytoplasmic m embrane. The correlation between production of and/or immunity to nisi n and sensitivity to carnocin of L. lactis subsp. lactis strains was f urther investigated. Several transformed L, lactis subsp. lactis strai ns carrying a fragment of the nisin gene cluster were tested for their sensitivity to carnocin U149 and their immunity to nisin. The results suggest that NisP, which is one of the membrane-associated proteins i nvolved in the production of nisin acts as receptor for carnocin U149. This may facilitate the binding and/or insertion of carnocin U149 int o the cytoplasmic membrane thus increasing its bactericidal activity. Lantibiotic-producing and non-producing mutants of Staphylococcus epid ermidis and Lactobacillus sake did not show a difference in sensitivit y to carnocin U149. The proposed receptor-mediated action of carnocin U149 at the cytoplasmic membrane therefore seems to be specific for th e nisin-producing strains.