Mode of action of the two-component bacteriocin lactocin 705

CASTELLANO, PATRICIA; CUOZZO, SERGIO; SESMA, FERNANDO; RAÚL RAYA AND GRACIELA VIGNOLO

Egmond aan Zee, The Netherlands

Simposio; Seventh Symposium on Lactic Acid Bacteria-Genetics, Metabolism and Applications; 2002

Federation of European Microbiological Societies and netherlands Institute for Microbiology

Lactocin 705 is a two-peptide bacteriocin produced by Lactobacillus casei CRL705, a strain isolated from dry fermented sausage. The mechanism of the two components of lactocin 705, of 33 amino acid residues each and named Lac705a and Lac705b, has been studied against sensitive cells of Lactobacillus plantarum CRL691 using chemically synthetized peptides. Lactocin 705 showed a bactericide effect on CRL691 cells. A different response was observed when the peptides were added separately to a diluted but still active supernatant of L. casei CRL705. While Lac705b potentiated the antimicrobial effect of the diluted supernatant, Lac705a protected CRL691 cells from inhibition. Electron microscopy of sensitive cells treated with Lac705a plus Lac705b, showed that the cell wall of CRL691 was severely damaged, with mesosome-like membranous formations protruding into the cytoplasm. A similar effect, although less pronounced, was also observed when Lac705b, but not Lac705a, was added alone to the cell suspension, suggesting that Lac705b is the active component of lactocin 705. The effect on the main components of the proton motive force (PMF), the membrane potential (DY) and the pH gradient (DpH), of Lactobacillus plantarun CRL691 were studied. The addition of both peptides to cells of L. plantarun dissipated both component of PMF. Energized membrane, obtained after the addition of 100 mM of glucose were more susceptible to lactocin 705 action. When the role of various ions on sensitive cells were analyzed only Ca++ ions exhibited a protective effect against lactocin 705. The data suggest that the presence of a PMF promotes the interaction of the bacteriocin with the cytoplasmic membrane of energized cells, leading to pore formation which allow for the efflux of ions. These effects cause growth inhibition and result in the ultimate death of lactocin 705-sensitive cells.