title: Knockout of the alanine racemase gene in Lactobacillus plantarum results in septation defects and cell wall perforation.
abstract: A stable mutant of Lactobacillus plantarum deficient in alanine racemase (Alr) was constructed by two successive homologous recombination steps. When the mutant was supplemented with D-alanine, growth and viability were unaffected. Surprisingly, deprivation of d-alanine during exponential growth did not result in a rapid and extensive lysis as observed in Alr-deficient strains of Escherichia coli or Bacillus subtilis. Rather, the starved mutant cells underwent a growth arrest and were gradually affected in viability with a decrease in colony forming units over 99% in less than 24 h. Additionally, fluorescent techniques demonstrated a loss of cell envelope integrity in the starved cells. Prolonged d-alanine starvation resulted in cells with an aberrant morphology. Scanning and transmission electron microscopy analyses revealed an increase in cell length, deficiencies in septum formation, thinning of the cell envelope and perforation of the cell wall in the septum region. We discuss the involvement of peptidoglycan hydrolases in these phenotypic defects in the context of the crucial role played by D-alanine in peptidoglycan biosynthesis and teichoic acids substitution.
authors.affiliation: Université catholique de Louvain, Institut des Sciences de la Vie (ISV), Unité de Génétique, B-1348 Louvain-La-Neuve, Belgium.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Palumbo
authors.forename: Christine F
authors.initials: CF
authors.lastname: Favier
authors.forename: Marie
authors.initials: M
authors.lastname: Deghorain
authors.forename: Pier Sandro
authors.initials: PS
authors.lastname: Cocconcelli
authors.forename: Corinne
authors.initials: C
authors.lastname: Grangette
authors.forename: Annick
authors.initials: A
authors.lastname: Mercenier
authors.forename: Elaine E
authors.initials: EE
authors.lastname: Vaughan
authors.forename: Pascal
authors.initials: P
authors.lastname: Hols
mesh_terms: D000409:Alanine / Q000378:metabolism; D000411:Alanine Racemase / Q000235:genetics*; D001412:Bacillus subtilis / Q000235:genetics / Q000254:growth & development; D001433:Bacteriolysis / Q000235:genetics; D002473:Cell Wall / Q000378:metabolism* / Q000648:ultrastructure*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development; D017353:Gene Deletion; D005798:Genes, Bacterial; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D007778:Lactobacillus / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development / Q000648:ultrastructure; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D010457:Peptidoglycan / Q000096:biosynthesis; D010539:Permeability; D013682:Teichoic Acids / Q000378:metabolism
chemical_list: D010457:Peptidoglycan; D013682:Teichoic Acids; D007770:L-Lactate Dehydrogenase; D000411:Alanine Racemase; D000409:Alanine