Class II sec-dependent bacteriocin

Because of their potential usefulness as natural food preservatives, increased interest has focused on bacteriocins from lactic acid bacteria. Mesentericin Y105 is a small non-lantibiotic bacteriocin (class II) encoded within a 35 kb plasmid from Leuconostoc mesenteroides Y105 and it is active against Listeria monocytogenes. Using reverse genetic methodologies, an 8 kb DraII fragment has been cloned that contains the mesentericin Y105 structural gene, mesY, which encodes a precursor of the bacteriocin with a 24 amino acid N-terminal extension ending with a Gly-Gly motif upstream of the cleavage site, which is typical of class II bacteriocins. Four other putative genes are associated with mesY within two divergent putative operons. In addition to mesY, the first putative operon is predicted to encode a protein, similar to that encoded by ORF2 in the leucocin A operon, whose function remains to be elucidated. The second putative operon contains three ORFs, two of which, mesD and mesE, encode proteins that resemble ATP-dependent transporters and accessory factors, respectively. For three other class II bacteriocin systems (lactococcin A, pediocin PA-1, colicin V), these proteins have been shown to be involved in bacteriocin secretion independently of the general sec-dependent secretion pathway. The last putative gene (mesC) does not resemble any previously characterized gene. Results concerning the heterologous expression of the cloned mesY in Lactobacillus johnsonii NCK64 suggest that the maturation and secretion functions dedicated to lactacin F (another class II bacteriocin) are efficient for mesentericin Y105 as well. This characteristic may be of great interest in the development of industrial fermentation starters producing multiple bactericidal activities.

A large number of new bacteriocins in lactic acid bacteria (LAB) has been characterized in recent years. Most of the new bacteriocins belong to the class II bacteriocins which are small (30-100 amino acids) heat- stable and commonly not post-translationally modified. While most bacteriocin producers synthesize only one bacteriocin, it has been shown that several LAB produce multiple bacteriocins (2-3 bacteriocins). Based on common features, some of the class II bacteriocins can be divided into separate groups such as the pediocin-like and strong anti-listeria bacteriocins, the two-peptide bacteriocins, and bacteriocins with a sec-dependent signal sequence. With the exception of the very few bacteriocins containing a sec-dependent signal sequence, class II bacteriocins are synthesized in a preform containing an N-terminal double-glycine leader. The double-glycine leader-containing bacteriocins are processed concomitant with externalization by a dedicated ABC-transporter which has been shown to possess an N-terminal proteolytic domain. The production of some class II bacteriocins (plantaricins of Lactobacillus plantarum C11 and sakacin P of Lactobacillus sake) have been shown to be transcriptionally regulated through a signal transduction system which consists of three components: an induction factor (IF), histidine protein kinase (HK) and a response regulator (RR). An identical regulatory system is probably regulating the transcription of the sakacin A and carnobacteriocin B2 operons. The regulation of bacteriocin production is unique, since the IF is a bacteriocin-like peptide with a double-glycine leader processed and externalized most probably by the dedicated ABC-transporter associated with the bacteriocin. However, IF is not constituting the bacteriocin activity of the bacterium, IF is only activating the transcription of the regulated class II bacteriocin gene(s). The present review discusses recent findings concerning biosynthesis, genetics, and regulation of class II bacteriocins.