Kinetic studies of the action of lactacin F, a bacteriocin produced by Lactobacillus johnsonii that forms poration complexes in the cytoplasmic membrane

Abstract

The bacteriocin lactacin F is bactericidal against Lactobacillus delbrueckii, Lactobacillus helveticus, and Enterococcus faecalis. Activity against L. delbrueckii was recently shown to be dependent on two peptides, LafA and LafX, which are encoded within the lactacin F operon (T. R. Klaenhammer, FEMS Microbiol. Rev. 12:39-87, 1993). It has been proposed that two peptides form an active lactacin F complex. In this study, the action of lactacin F against E. faecalis ATCC 19443 and the effects of various environmental parameters were investigated in detail. Addition of lactacin F induced the loss of K+ from cells of L. delbrueckii, Lactobacillus johnsonii 88-4, and E. faecalis, while the lactacin F producer L. johnsonii VPI 11088 was not affected by the bacteriocin. Lactacin F caused an immediate loss of cellular K+, depolarization of the cytoplasmic membrane, and hydrolysis of internal ATP in E. faecalis. Lactacin F induced loss of K+ in 3,3',4',5- tetrachlorosalicylanilide-treated cells, indicating that pores are formed in the absence of a proton motive force. ATP hydrolysis was not due to dissipation of the proton motive force but was most likely caused by efflux of inorganic phosphate, resulting in a shift of the ATP hydrolysis equilibrium. Action of lactacin F was optimal at acidic pH values and was reduced in the presence of di- and trivalent cations. The lanthanide gadolinium (Gd3+) prevented action of lactacin F completely at a concentration of 0.2 mM. Lactacin F-induced loss of cell K+ was severely reduced at low temperatures, presumably as a result of increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30°C, lactacin F action was prevented at temperatures below 10°C, and increasing lag times were observed at temperatures below 25°C. An examination of parameters that affected lactacin F action provided insights into the possible mechanisms by which peptide bacteriocins interact with the cytoplasmic membrane and form poration complexes.