Prophage induction in Lactococcus lactis by the bacteriocin Lactococcin 972

Lactococcin 972 (Lcn972) is a non-pore forming bacteriocin with a narrow spectrum of activity restricted to Lactococcus. Lcn972 inhibits the incorporation of cell wall precursors in the septum area, thereby inhibiting cell division. In this work, an additional inhibitory effect is described, namely, the induction of the lytic cycle of resident prophages in the lysogenic strain L. lactis IPLA 513. Lcn972 triggered the release of prophages in a concentration-dependent fashion. The extent of prophage induction was influenced by the physiological status of the cultures, being maximal at the early exponential growth phase. A microtiter based protocol was designed and the induction ability of several antimicrobials was compared. Prophages were activated by all cell wall biosynthesis inhibitors tested, although the levels of induction were lower than those obtained after activation of the SOS response. As far as we know, this is the first report of prophage induction by an antimicrobial peptide. Since Lcn972 is active against L. lactis strains currently used in commercial starters, promising applications for dairy fermentations are discussed.