title: Mechanism of bactericidal activity of microcin L in Escherichia coli and Salmonella enterica.
abstract: For the first time, the mechanism of action of microcin L (MccL) was investigated in live bacteria. MccL is a gene-encoded peptide produced by Escherichia coli LR05 that exhibits a strong antibacterial activity against related Enterobacteriaceae, including Salmonella enterica serovars Typhimurium and Enteritidis. We first subcloned the MccL genetic system to remove the sequences not involved in MccL production. We then optimized the MccL purification procedure to obtain large amounts of purified microcin to investigate its antimicrobial and membrane properties. We showed that MccL did not induce outer membrane permeabilization, which indicated that MccL did not use this way to kill the sensitive cell or to enter into it. Using a set of E. coli and Salmonella enterica mutants lacking iron-siderophore receptors, we demonstrated that the MccL uptake required the outer membrane receptor Cir. Moreover, the MccL bactericidal activity was shown to depend on the TonB protein that transduces the proton-motive force of the cytoplasmic membrane to transport iron-siderophore complexes across the outer membrane. Using carbonyl cyanide 3-chlorophenylhydrazone, which is known to fully dissipate the proton-motive force, we proved that the proton-motive force was required for the bactericidal activity of MccL on E. coli. In addition, we showed that a primary target of MccL could be the cytoplasmic membrane: a high level of MccL disrupted the inner membrane potential of E. coli cells. However, no permeabilization of the membrane was detected.
authors.affiliation: Laboratoire Littoral Environnement Sociétés, UMR 6250 CNRS-ULR, Université de La Rochelle, UFR Sciences, Bât. Marie Curie, Avenue Michel Crépeau, 17042 La Rochelle Cedex 01, France.
authors.forename: Natacha
authors.initials: N
authors.lastname: Morin
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lanneluc
authors.forename: Nathalie
authors.initials: N
authors.lastname: Connil
authors.forename: Marie
authors.initials: M
authors.lastname: Cottenceau
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Pons
authors.forename: Sophie
authors.initials: S
authors.lastname: Sablé
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001430:Bacteriocins / Q000494:pharmacology*; D004751:Enteritis / Q000382:microbiology; D004926:Escherichia coli / Q000187:drug effects; D008826:Microbial Sensitivity Tests; D019779:Salmonella enterica / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D001430:Bacteriocins; C020411:microcin