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Personne :
Bissonnette, Frédéric.

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Bissonnette

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Frédéric.

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Département de biochimie et de microbiologie, Faculté des sciences et de génie, Université Laval

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  • PublicationRestreint
    Characterization of mesophilic mixed starter cultures used for the manufacture of aged cheddar cheese
    (American Dairy Science Science, 2000-04-01) Lamoureux, Maryse.; Moineau, Sylvain; Deveau, Hélène; Labrie, Simon; Bissonnette, Frédéric.
    Seventy-one different Lactococcus lactis subsp. cremoris strains were isolated from seven mesophilic mixed starters used in the manufacture of aged Cheddar cheese in Canada. Based on plasmid profiles and growth in milk (with or without glucose, Casamino Acids or both), two mixed starters were highly heterogeneous, containing at least 18 to 24 distinct L. lactis strains. Three mixed starters were comprised of seven to nine strains, whereas two starters were relatively homogeneous, containing two or three strains. Many strains with similar plasmid profiles behaved differently during growth in milk, indicating variability in the pheno-types. Only 20% of the strains could grow in plain milk, whereas 30% could not grow in milk supplemented with glucose and Casamino Acids. Twenty-five lactococcal bacteriophages were also isolated from whey samples with single strains as hosts. Eighteen phages belonged to the 936 species and seven to the c2 species. Thirteen strains were insensitive to all 25 phages. Almost all sensitive strains were phage species-specific. The 936-like phages had a broader host range.
  • PublicationAccès libre
    Characterization of the cro-ori region of the Streptococcus thermophilus virulent bacteriophage DT1
    (American Society for Microbiology, 2005-03-03) Vadeboncoeur, Christian; Tremblay, Denise; Frenette, Michel; Cochu, Armelle; Moineau, Sylvain; Lamothe, Geneviève; Duplessis, Martin; Bissonnette, Frédéric.; Lévesque, Céline
    The virulent cos-type Streptococcus thermophilus phage DT1 was previously isolated from a mozzarella whey sample, and its complete genomic sequence is available. The putative ori of phage DT1 is characterized by three inverted and two direct repeats located in a noncoding region between orf36 and orf37. As the replication ability of the putative ori and flanking genes could not be established, its ability to confer phage resistance was tested. When ori is cloned on a high-copy-number plasmid, it provides protection to S. thermophilus strains against phage infection during milk fermentation. This protection is phage specific and strain dependent. Then, a detailed transcriptional map was established for the region located between the cro-like gene (orf29) and the ori. The results of the Northern blots indicated that the transcription of this region started 5 min after the onset of phage infection. Comparative analysis of the expression of the cro-ori region in the three S. thermophilus cos-type phages DT1, Sfi19 (virulent), and Sfi21 (temperate) reveals significant differences in the number and size of transcripts. The promoter upstream of orf29 was further investigated by primer extension analysis, and its activity was confirmed by a chloramphenicol acetyltransferase assay, which showed that the phage promoter is more efficient than the constitutive bacterial promoter of the S. thermophilus operon encoding the general proteins of the phosphoenolpyruvate:sugar phosphotransferase system. However, the phage promoter is less efficient than the pts promoter in Lactococcus lactis and in Escherichia coli.
  • PublicationRestreint
    Characterization of the two-component abortive phage infection mechanism AbiT from Lactococcus lactis
    (American Society for Microbiology, 2002-11-01) Dion, Éric; Bouchard, Julie; Bissonnette, Frédéric.
    During the production of fermented dairy products, virulent bacteriophages infecting Lactococcuslactis 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 and 10) 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 theplasmid 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 map pingindicated that AbiT is likely to act at a later stage of the phage lytic cycle.