ABSTRACT
Nisin is a post-translationally modified antimicrobial peptide produced by Lactococcus lactis which binds to lipid II in the membrane to form pores and inhibit cell-wall synthesis. A nisin-resistant (Nis(R)) strain of L. lactis, which is able to grow at a 75-fold higher nisin concentration than its parent strain, was investigated with respect to changes in the cell wall. Direct binding studies demonstrated that less nisin was able to bind to lipid II in the membranes of L. lactis Nis(R) than in the parent strain. In contrast to vancomycin binding, which showed ring-like binding, nisin was observed to bind in patches close to cell-division sites in both the wild-type and the Nis(R) strains. Comparison of modifications in lipoteichoic acid of the L. lactis strains revealed an increase in d-alanyl esters and galactose as substituents in L. lactis Nis(R), resulting in a less negatively charged cell wall. Moreover, the cell wall displays significantly increased thickness at the septum. These results indicate that shielding the membrane and thus the lipid II molecule, thereby decreasing abduction of lipid II and subsequent pore-formation, is a major defence mechanism of L. lactis against nisin.
Subject(s)
Alanine/metabolism , Cell Wall/metabolism , Drug Resistance, Bacterial , Lactococcus lactis/drug effects , Lactococcus lactis/metabolism , Lipopolysaccharides/metabolism , Nisin/pharmacology , Teichoic Acids/metabolism , Anti-Bacterial Agents/metabolism , Anti-Bacterial Agents/pharmacology , Cell Division , Cell Wall/drug effects , Cell Wall/ultrastructure , Lactococcus lactis/genetics , Lactococcus lactis/growth & development , Lipopolysaccharides/chemistry , Microscopy, Confocal , Microscopy, Electron , Nisin/genetics , Nisin/metabolism , Teichoic Acids/chemistry , Vancomycin/metabolism , Vancomycin/pharmacologyABSTRACT
Lantibiotics are polycyclic peptides containing unusual amino acids, which have binding specificity for bacterial cells, targeting the bacterial cell wall component lipid II to form pores and thereby lyse the cells. Yet several members of these lipid II-targeted lantibiotics are too short to be able to span the lipid bilayer and cannot form pores, but somehow they maintain their antibacterial efficacy. We describe an alternative mechanism by which members of the lantibiotic family kill Gram-positive bacteria by removing lipid II from the cell division site (or septum) and thus block cell wall synthesis.
