title: Characterization of the two-component abortive phage infection mechanism AbiT from Lactococcus lactis.
abstract: During the production of fermented dairy products, virulent bacteriophages infecting Lactococcus lactis can delay or stop the milk acidification process. A solution to this biological problem consists of introducing natural phage barriers into the strains used by the dairy industry. One such hurdle is called abortive infection (Abi) and causes premature cell death with no or little phage progeny. Here, we describe the isolation and characterization of a novel Abi mechanism encoded by plasmid pED1 from L. lactis. The system is composed of two constitutively cotranscribed genes encoding putative proteins of 127 and 213 amino acids, named AbiTi and AbiTii, respectively. Site-directed mutagenesis indicated that a hydrophobic region at the C-terminal extremity of AbiTi is essential to the antiphage phenotype. The AbiT system is effective against phages of the 936 and P335 species (efficiency of plaquing between 10(-5) and 10(-7)) and causes a 20-fold reduction in the efficiency to form centers of infection as well as a 10- to 12-fold reduction in the burst size. Its efficacy could be improved by raising the plasmid copy number, but changing the intrinsic ratio of AbiTi and AbiTii did not greatly affect the antiphage activity. The monitoring of the intracellular phage infection process by DNA replication, gene expression, and electron microscopy as well as the study of phage mutants by genome mapping indicated that AbiT is likely to act at a later stage of the phage lytic cycle.
authors.affiliation: Department of Biochemistry and Microbiology, Faculté des Sciences et de Génie, Groupe de Recherche en Ecologie Buccale, Faculté de Médecine Dentaire, Université Laval, Québec, Canada G1K 7P4.
authors.forename: Julie D
authors.initials: JD
authors.lastname: Bouchard
authors.forename: Eric
authors.initials: E
authors.lastname: Dion
authors.forename: Frédéric
authors.initials: F
authors.lastname: Bissonnette
authors.forename: Sylvain
authors.initials: S
authors.lastname: Moineau
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001435:Bacteriophages / Q000235:genetics / Q000472:pathogenicity*; D001483:Base Sequence; D003001:Cloning, Molecular; D013294:Lactococcus lactis / Q000378:metabolism / Q000821:virology*; D008242:Lysogeny; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010957:Plasmids
chemical_list: D001426:Bacterial Proteins