Complete sequence of the enterocin Q-encoding plasmid pCIZ2 from the multiple bacteriocin producer Enterococcus faecium L50 and genetic characterization of enterocin Q production and immunity

The locations of the genetic determinants for enterocin L50 (EntL50A and EntL50B), enterocin Q (EntQ), and enterocin P (EntP) in the multiple bacteriocin producer Enterococcus faecium strain L50 were determined. These bacteriocin genes occur at different locations; entL50AB (encoding EntL50A and EntL50B) are on the 50-kb plasmid pCIZ1, entqA (encoding EntQ) is on the 7.4-kb plasmid pCIZ2, and entP (encoding EntP) is on the chromosome. The complete nucleotide sequence of pCIZ2 was determined to be 7,383 bp long and contains 10 putative open reading frames (ORFs) organized in three distinct regions. The first region contains three ORFs: entqA preceded by two divergently oriented genes, entqB and entqC. EntqB shows high levels of similarity to bacterial ATP-binding cassette (ABC) transporters, while EntqC displays no significant similarity to any known protein. The second region encompasses four ORFs (orf4 to orf7), and ORF41 and ORF5 display high levels of similarity to mobilization proteins from E. faecium and Enterococcus faecalis. In addition, features resembling a transfer origin region (oriT) were found in the promoter area of orf4. The third region contains three ORFs (orf8 to orf10), and ORF8 and ORF9 exhibit similarity to the replication initiator protein RepE from E. faecalis and to RepB proteins, respectively. To clarify the minimum requirement for EntQ synthesis, we subcloned and heterologously expressed a 2,371-bp fragment from pCIZ2 that encompasses only the entqA, entqB, and entqC genes in Lactobacillus sakei, and we demonstrated that this fragment is sufficient for EntQ production. Moreover, we also obtained experimental results indicating that EntqB is involved in ABC transporter-mediated EntQ secretion, while EntqC confers immunity to this bacteriocin.