Some strains of lactic acid bacteria secrete antimicrobial peptides which could be used as natural preservatives in food and feed fermentations. These so-called bacteriocins are secreted via a dedicated sec-independent secretion system consisting of (at least) two proteins. The aim of the project is to unravel the mechansim of bacteriocin secretion by determining the specificity of and the interaction between the two components of the transport system. By reciprocally exchanging the four proteins involved in the secretion of lactococcin A and pediocin PA- I, the specificity of both transport systems will be unravelled. By making protein fusions and by isolating antibodies against the proteins under study, the interaction between the proteins of each system will be analyzed. Various mutation/complementation strategies will further pinpoint the interacting domains.