title: Involvement of the major capsid protein and two early-expressed phage genes in the activity of the lactococcal abortive infection mechanism AbiT.
abstract: The dairy industry uses the mesophilic, Gram-positive, lactic acid bacterium (LAB) Lactococcus lactis to produce an array of fermented milk products. Milk fermentation processes are susceptible to contamination by virulent phages, but a plethora of phage control strategies are available. One of the most efficient is to use LAB strains carrying phage resistance systems such as abortive infection (Abi) mechanisms. Yet, the mode of action of most Abi systems remains poorly documented. Here, we shed further light on the antiviral activity of the lactococcal AbiT system. Twenty-eight AbiT-resistant phage mutants derived from the wild-type AbiT-sensitive lactococcal phages p2, bIL170, and P008 were isolated and characterized. Comparative genomic analyses identified three different genes that were mutated in these virulent AbiT-insensitive phage derivatives: e14 (bIL170 [e14(bIL170)]), orf41 (P008 [orf41(P008)]), and orf6 (p2 [orf6(p2)] and P008 [orf6(P008)]). The genes e14(bIL170) and orf41(P008) are part of the early-expressed genomic region, but bioinformatic analyses did not identify their putative function. orf6 is found in the phage morphogenesis module. Antibodies were raised against purified recombinant ORF6, and immunoelectron microscopy revealed that it is the major capsid protein (MCP). Coexpression in L. lactis of ORF6(p2) and ORF5(p2), a protease, led to the formation of procapsids. To our knowledge, AbiT is the first Abi system involving distinct phage genes.
authors: Groupe de Recherche en Écologie Buccale, Faculté de Médecine Dentaire, Faculté des Sciences et de Génie, Université Laval, Quebec City, Quebec, Canada.
authors: Simon J
authors: SJ
authors: Labrie
authors: Denise M
authors: DM
authors: Tremblay
authors: Maxim
authors: M
authors: Moisan
authors: Manuela
authors: M
authors: Villion
authors: Alfonso H
authors: AH
authors: Magadán
authors: Valérie
authors: V
authors: Campanacci
authors: Christian
authors: C
authors: Cambillau
authors: Sylvain
authors: S
authors: Moineau
mesh_terms: D001435:Bacteriophages / Q000235:genetics* / Q000254:growth & development* / Q000502:physiology; D036022:Capsid Proteins / Q000378:metabolism*; D004252:DNA Mutational Analysis; D015967:Gene Expression Regulation, Viral; D013294:Lactococcus lactis / Q000821:virology*; D016253:Microscopy, Immunoelectron; D014771:Virion / Q000648:ultrastructure; D014779:Virus Replication
chemical_list: D036022:Capsid Proteins