KINETIC-STUDIES OF THE ACTION OF LACTACIN-F, A BACTERIOCIN PRODUCED BY LACTOBACILLUS-JOHNSONII THAT FORMS PORATION COMPLEXES IN THE CYTOPLASMIC MEMBRANE

The bacteriocin lactacin F is bactericidal against Lactobacillus delbr ueckii, Lactobacillus helveticus, and Enterococcus faecalis. Activity against L. delbrueckii was recently shown to be dependent on two pepti des, LafA and LafX, which are encoded within the lactacin F operon (T. R. Klaenhammer, FEMS Microbiol. Rev. 12:39-87, 1993). It has been pro posed that two peptides form an active lactacin F complex. In this stu dy, the action of lactacin F against E. faecalis ATCC 19443 and the ef fects of various environmental parameters were investigated in detail. Addition of lactacin F induced the loss of K+ from cells of L. delbru eckii, Lactobacillus johnsonii 88-4, and E. faecalis, while the lactac in F producer L. johnsonii VPI 11088 was not affected by the bacterioc in. Lactacin F caused an immediate loss of cellular KC, depolarization of the cytoplasmic membrane, and hydrolysis of internal ATP in E. fae calis. Lactacin F induced loss of K+ in 3,3',4',5-tetrachlorosalicylan ilide-treated cells, indicating that pores are formed in the absence o f a proton motive force. ATP hydrolysis was not due to dissipation of the proton motive forte but was most likely caused by efflux of inorga nic 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 gadoliniu m (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 a t 30 degrees C, lactacin F action was prevented at temperatures below 10 degrees C, and increasing lag times were observed at temperatures b elow 25 degrees C. An examination of parameters that affected lactacin F action provided insights into the possible mechanisms by which pept ide bacteriocins interact with the cytoplasmic membrane and form porat ion complexes.