AimsCharacterization of the biosynthesis (secretion and immunity) of lactococcin Z. Methods and ResultsLactococcin Z is produced by Lactococcus lactisQU 7. DNA sequence analysis revealed that the lactococcin Z gene cluster (c. 51kb) includes four genes encoding putative biosynthetic proteins, LczB (self-immunity protein), LczC (an ABC transporter) and LczD (a transport accessory protein), besides the previously identified LczA. LczB showed 255% identity to LciA, the lactococcin A immunity protein, while LczC and LczD had 937 and 953% identities, respectively, to corresponding proteins of lactococcin A. Heterologous expression of various combinations of the four genes indicated that lczB confers self-immunity against lactococcin Z, and that the four genes are necessary to produce lactococcin Z. However, LczB and LciA showed no cross-immunity to lactococcins A and Z respectively. ConclusionsThe results verified that LczB is the lactococcin Z immunity protein, and LczC is responsible for lactococcin Z secretion in a manner dependent on LczD expression. Significance and Impact of the StudyThe biosynthesis (secretion and immunity) of a new Lactococcus-specific bacteriocin, lactococcin Z, was characterized. Moreover, the results suggested that lactococcin Z has different immunity and action mechanisms from other Lactococcus-specific bacteriocins.