A C-terminal disulfide bridge in pediocin-like bacteriocins renders bacteriocin activity less temperature dependent and is a major determinant of theantimicrobial spectrum

Several lactic acid bacteria produce so-called pediocin-like bacteriocins t hat share sequence characteristics, but differ in activity and target cell specificity. The significance of a C-terminal disulfide bridge present in o nly a few of these bacteriocins was studied by site-directed mutagenesis of pediocin PA-1 (which naturally contains the bridge) and sakacin P (which l acks the bridge). Introduction of the C-terminal bridge into sakacin P broa dened the target cell specificity of this bacteriocin, as illustrated by th e fact that the mutants were 10 to 20 times more potent than the wild-type toward certain indicator strains, whereas the potency toward other indicato r strains remained essentially unchanged. Like pediocin PA-1, disulfide-con taining sakacin P mutants had the same potency at 20 and 37 degrees C, wher eas wild-type sakacin P was approximately 10 times less potent at 37 degree s C than at 20 degrees C. Reciprocal effects on target cell specificity and the temperature dependence of potency were observed upon studying the effe ct of removing the C-terminal disulfide bridge from pediocin PA-1 by Cys--> Ser mutations. These results clearly show that a C-terminal disulfide bridg e in pediocin-like bacteriocins contributes to widening of the antimicrobia l spectrum as well as to higher potency at elevated temperatures. Interesti ngly, the differences between sakacin P and pediocin PA-1 in terms of the t emperature dependency of their activities correlated well with the optimal temperatures for bacteriocin production and growth of the bacteriocin-produ cing strain.