Cloning and expression of the genes involved in the production of and immunity against the bacteriocin lacticin RM.

The production of lacticin RM, a novel bacteriocin produced by Lactococcus lactis subsp. lactis EZ26, is associated with the presence of a 6-kb plasmid, pHU1. The information necessary for lacticin RM production and immunity was localized to a 2.5-kb SalI-Eco47III fragment. Sequencing analysis of this fragment revealed the presence of six open reading frames (ORFs). Deletion and mutation analyses showed that orfX and orfY are not required for lacticin RM production or immunity, whereas the other ORFs (lacA, lacF, lacG and lacI) are necessary for the bacteriocin's production. Transcription analysis indicated that lacA, lacF and lacG are organized in an operon. lacA is probably the lacticin RM structural gene. It putatively encodes a 134-amino acid peptide, and it does not share homology with known bacteriocins. The deduced LacG protein is hydrophobic and consists of six potential trans-membrane helices. lacF encodes a conserved ATP-binding domain homologous to ABC transporters known in bacteriocin immunity systems. LacF and LacG may form an active ABC transporter. Gene-disruption mutations indicated that both are required for immunity against lacticin RM. lacI encodes a small cationic protein, which is required for the production of and immunity to lacticin RM. Protection was obtained only when lacF, lacG and lacI were present together.