Positive role of peptidoglycan breaks in lactococcal biofilm formation

Mol Microbiol. 2002 Oct;46(1):235-43. doi: 10.1046/j.1365-2958.2002.03160.x.

Abstract

Bacterial attachment to solid matrices depends on adhesive molecules present on the cell surface. Here we establish a positive correlation between peptidoglycan (PG) breaks, rather than particular molecules, and biofilm-forming capacity in the Gram-positive bacterium Lactococcus lactis. The L. lactis acmA strain, which is defective in PG hydrolase, adhered less efficiently than the wild-type (wt) strain to different solid surfaces and was unable to form biofilms. These phenotypes were abolished by addition of lysozyme, a PG hydrolytic enzyme. Thus, the presence of PG breaks introduced by PG hydrolase, and not the AcmA protein itself, appears to be responsible for biofilm formation. Two different genetic screens confirmed the importance of PG breaks in L. lactis biofilm formation. Using the chain-forming ability of the acmA strain as a phenotypic indicator of PG integrity, we selected for insertional mutants generating short chains. Five independent mutants were all mapped to ponA, which encodes the PG synthesis enzyme PBP1A. Double acmA ponA mutants displayed increased adhesion and biofilm-forming capacity. Direct selection for strains with increased biofilm-forming capacity resulted in the isolation of another five mutations in ponA. Based on these results, we conclude that PG breaks are important for both adhesion and biofilm formation in L. lactis.

MeSH terms

  • Bacterial Adhesion
  • Bacterial Proteins*
  • Biofilms / growth & development*
  • Carrier Proteins*
  • Cell Wall / chemistry
  • Hexosyltransferases / genetics
  • Hexosyltransferases / metabolism
  • In Situ Hybridization, Fluorescence
  • Lactococcus lactis / genetics
  • Lactococcus lactis / growth & development*
  • Lactococcus lactis / metabolism
  • Microscopy, Electron, Scanning
  • Multienzyme Complexes / genetics
  • Multienzyme Complexes / metabolism
  • Muramoylpentapeptide Carboxypeptidase*
  • Mutation
  • N-Acetylmuramoyl-L-alanine Amidase / genetics
  • N-Acetylmuramoyl-L-alanine Amidase / metabolism
  • Penicillin-Binding Proteins
  • Peptidoglycan / metabolism*
  • Peptidyl Transferases / genetics
  • Peptidyl Transferases / metabolism

Substances

  • Bacterial Proteins
  • Carrier Proteins
  • Multienzyme Complexes
  • Penicillin-Binding Proteins
  • Peptidoglycan
  • Peptidyl Transferases
  • Hexosyltransferases
  • Muramoylpentapeptide Carboxypeptidase
  • N-Acetylmuramoyl-L-alanine Amidase