Molecular analysis of the bacteriocin-encoding plasmid pDGL1 from Enterococcus durans and genetic characterization of the durancin GL locus.

Enterococci constitute a significant component of the lactic acid bacteria normally present in the intestinal microflora and include strains that produce bacteriocins. The genetic determinants for durancin GL in Enterococcus durans 41D were identified on the 8347 bp plasmid pDGL1 by plasmid curing experiments. pDGL1 contained nine putative ORFs, with ORF1 and ORF2 encoding plasmid replication proteins, and ORF3 and ORF6 showing high similarity to genes encoding mobilization proteins. The predicted protein encoded by ORF4 showed 74 % identity to BacA, a bacteriocin produced by Enterococcus faecalis. The deduced DurA protein contained the conserved motif YYGNG, suggesting that durancin GL is a typical subclass IIa bacteriocin. ORF5 was shown to share 85 % identity to the immunity protein BacB of Enterococcus faecalis. ORF9 displayed 87 % sequence identity to a conserved hypothetical protein of unknown function. To further clarify the minimum requirement for durancin GL production, a 547 bp fragment containing the durAB gene was fitted with the Streptococcus thermophilus P(2201) promoter and then subcloned and heterologously expressed in S. thermophilus ST128. The result demonstrated that the cloned fragment contained all the genetic components required for durancin GL production.