Genetic analysis of the plantaricin EFI locus of Lactobacillus plantarum PCS20 reveals an unusual plantaricin E gene sequence as a result of mutation

Abstract

Lactobacillus plantarum strains produce a variety of chromosomally encoded bacteriocins and often multiple bacteriocins are encoded by a single strain. In this study, the genetic loci for bacteriocin production of L. plantarum strains BFE 5092 and PCS20 were studied. These strains were investigated for their possible application as protective cultures in food preservation. The bacteriocin locus of strain BFE 5092 showed remarkable similarity to the plantaricin loci previously described for L. plantarum strains C11 and WCFS1. However, the locus of the L. plantarum PCS20 strain was unusual in that it showed an interesting mutation as a result of deletions within the plnE gene. These deletions led to a hypothetically produced peptide which is 2 amino acids shorter than plantaricin E. Furthermore, it differs by 24 amino acids, while it shares 30 identical amino acids i.e., 15 at the amino end and 15 at the carboxyl end of the hypothetical peptide. As a consequence, the amino acid sequence is changed such that a double-glycine-type leader peptide would not be encoded. This raises the question whether a functional peptide is being produced, even though RT-PCR studies showed that the plnE gene is obviously expressed. Furthermore, a transposase gene was located upstream of the plnEFI gene cluster and was inserted into a bacteriocin regulatory gene, the histidine protein kinase gene. Taken together, these facts indicate a loss of plantaricin gene function in L. plantarum PCS20 as a result of transposition and mutation.