title: Isolation of Lactococcus lactis mutants simultaneously resistant to the cell wall-active bacteriocin Lcn972, lysozyme, nisin, and bacteriophage c2.
abstract: Lactococcin 972 (Lcn972) is a nonlantibiotic bacteriocin that inhibits cell wall biosynthesis by binding to lipid II. In this work, two mutants resistant to Lcn972, Lactococcus lactis D1 and D1-20, with high (>320 arbitrary units [AU]/ml) and low (80 AU/ml) susceptibilities, respectively, have been isolated. Resistance to Lcn972 did not impose a burden to growth under laboratory conditions, nor did it substantially alter the physicochemical properties of the cell surface. However, the peptidoglycan of the mutants featured a higher content of muropeptides with tripeptide side chains than the wild-type strain, linking for the first time peptidoglycan remodelling to bacteriocin resistance. Moreover, L. lactis lacking a functional D,D-carboxypeptidase DacA (i.e., with a high content of pentapeptide side chain muropeptides) was shown to be more susceptible to Lcn972. Cross-resistance to lysozyme and nisin and enhanced susceptibility to penicillin G and bacitracin was also observed. Intriguingly, the Lcn972-resistant mutants were not infected by the lytic phage c2 and less efficiently infected by phage sk1. Lack of c2 infectivity was linked to a 22.6-kbp chromosomal deletion encompassing the phage receptor protein gene pip. The deletion also included maltose metabolic genes and the two-component system (TCS) F. However, a clear correlation between these genes and resistance to Lcn972 could not be clearly established, pointing to the presence of as-yet-unidentified mutations that account for Lcn972 resistance.
authors.affiliation: Department of Technology and Biotechnology of Dairy Products, Instituto de Productos Lácteos de Asturias (IPLA-CSIC), Villaviciosa, Asturias, Spain.
authors.forename: Clara
authors.initials: C
authors.lastname: Roces
authors.forename: Pascal
authors.initials: P
authors.lastname: Courtin
authors.forename: Saulius
authors.initials: S
authors.lastname: Kulakauskas
authors.forename: Ana
authors.initials: A
authors.lastname: Rodríguez
authors.forename: Marie-Pierre
authors.initials: MP
authors.lastname: Chapot-Chartier
authors.forename: Beatriz
authors.initials: B
authors.lastname: Martínez
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001430:Bacteriocins / Q000494:pharmacology; D001435:Bacteriophages / Q000254:growth & development; D002473:Cell Wall / Q000737:chemistry* / Q000187:drug effects*; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000235:genetics; D013294:Lactococcus lactis / Q000187:drug effects* / Q000302:isolation & purification*; D009113:Muramidase / Q000378:metabolism; D009154:Mutation; D009561:Nisin / Q000494:pharmacology; D009842:Oligopeptides / Q000032:analysis; D010457:Peptidoglycan / Q000737:chemistry; D017384:Sequence Deletion
chemical_list: D000900:Anti-Bacterial Agents; D001430:Bacteriocins; D004269:DNA, Bacterial; D009842:Oligopeptides; D010457:Peptidoglycan; D009561:Nisin; D009113:Muramidase