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Plasmid content and bacteriocin production by five strains of Lactococcus lactis isolated from semi-hard homemade cheese

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In this study, the plasmid content and bacteriocin production of natural isolates of lactococci were investigated. Five bacteriocin producing lactococcal strains (Lactococcus lactis subsp. lactis BGMN1-2, BGMN1-3, BGMN1-5, BGMN1-6, and BGMN2-7) were isolated as nonstarter microflora of semi-hard homemade cheese and characterized. All isolates contained a number of plasmids. It was shown that lcnB structural genes for bacteriocin lactococcin B were located on large plasmids in all isolates. In the strains BGMN1-3 and BGMN1-5 proteinase prtP genes collocated with lcnB. Furthermore, these strains produced two additional bacteriocins (LsbA and LsbB) with genes responsible for their production and immunity located on the small rolling circle-replicating plasmid pMN5. Using deletion experiments of pMN5, minimal replicon of the plasmid and involvement of a bacteriocin locus in plasmid maintenance were identified. In addition, plasmid curing experiments showed that genes for catabolism or transport of 10 carbohydrates in the strain BGMN1-5 were plasmid located.Key words: lactococci, natural isolates, bacteriocin, plasmid curing.

Dans cette étude, le contenu plasmidique et la production de bactériocines par des isolats naturels de lactocoques furent examinés. Cinq souches de lactocoques produisant des bactériocines, Lactococcus lactis subsp. lactis BGMN1-2, BGMN1-3, BGMN1-5, BGMN1-6 et BGMN2-7, furent isolés dans la microflore secondaire de fromages maison à pâte semi dure et caractérisée. Les isolats contenaient un certain nombre de plasmides. Il fut démontré que les gènes structuraux lcnB de la bactériocine lactococcine B étaient situés sur des grands plasmides chez tous les isolats. Chez les souches BGMN1-3 et BGMN1-5, les gènes de la protéinase prtP étaient colocalisés avec lncB. De plus, les isolats BGMN1-3 et BGMN1-5 ont produit des bactériocines supplémentaires (LsbA et LsbB) dont les gènes responsables de la production et de leur immunité était situés sur le petit plasmide pMN5 qui se répliquait par cercle roulant. À l'aide d'expériences de délétion de pMN5, le réplicon minimal du plasmide et l'implication du locus de la bactériocine dans le maintien du plasmide furent identifiés. De plus, des expériences de cure plasmidique ont démontré que des gènes participant au catabolisme de dix glucides chez la souche BGMN1-5 était situés sur un plasmide.Mots clés : lactocoques, isolats naturels, bactériocines, cure plasmidique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2006-11-01

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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