Functional Characterization of a Composite Bacteriocin Locus from Malt Isolate Lactobacillus sakei 5

Lactobacillus sakei 5, isolated from malted barley, produces three bacteriocins. Genetic and functional analysis of the purified bacteriocins showed that this strain produces a plasmid-encoded bacteriocin that is identical to sakacin P, as well as two novel, chromosomally encoded bacteriocins, which were designated sakacin T and sakacin X. The structural genes specifying sakacin T and sakacin X are part of the sakacin TX locus, which consists of two adjacent but divergently oriented gene clusters. The first gene cluster includes stxP, stxR, stxK, and stxT, which, based on functional and comparative sequence analysis, are believed to encode an inducing peptide and proteins involved in regulation and secretion of these bacteriocins. The second gene cluster includes the structural and immunity genes for sakacin T, a class IIb two-peptide bacteriocin composed of SakTα and SakTβ, and sakacin X, a class IIa bacteriocin. Interestingly, a so-called transport accessory protein was absent from the locus, and based on our results it appears that a dedicated accessory protein is not required for processing and transport of sakacin T and sakacin X.