Characterization of the genetic locus responsible for production and immunity of carnobacteriocin A: the immunity gene confers cross-protection to enterocin B.

Carnobacteriocin A (CbnA) is a regulated bacteriocin produced by Carnobacterium piscicola LV17A that is encoded on a 72 kb plasmid. A 10.0 kb fragment from this plasmid that contained information necessary for bacteriocin production and immunity was cloned and sequenced. Genetic analysis showed the presence of the previously sequenced structural gene for CbnA, as well as genes encoding proteins homologous to dedicated bacteriocin transport proteins and proteins of three-component signal transduction systems. The induction factor (CbnX) was chemically synthesized and induced CbnA production at 10(-11) M or higher in a C. piscicola LV17A culture that had lost the ability to produce bacteriocin as a result of dilution. The gene cbiA for the immunity protein is not located in typical close proximity to the structural gene for CbnA and is encoded in the opposite orientation. CbiA has homology with EniB, the immunity protein for enterocin B that is also encoded in the opposite orientation to the bacteriocin gene. CbiA and EniB cross-protected against the corresponding bacteriocins.