Minisatellite polymorphism as a tool to distinguish closely related Lactococcus lactis strains

Authors

  • Pascal Quénée,

    1. Recherches Laitières et Génétique Appliquée – URLGA, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas Cedex, France
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  • Elodie Lepage,

    1. Recherches Laitières et Génétique Appliquée – URLGA, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas Cedex, France
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  • Woojin Scott Kim,

    1. School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia
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  • Gilles Vergnaud,

    1. Laboratoire GPMS, Institut de Génétique et Microbiologie, Bat 400, Universite Paris-Sud, 91405 Orsay Cedex, France
    2. Division d'Analyses Microbiologiques, Centre d'Etudes du Bouchet BP3, 91710 Vert le Petit, France
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  • Alexandra Gruss

    Corresponding author
    1. Recherches Laitières et Génétique Appliquée – URLGA, Institut National de la Recherche Agronomique, Domaine de Vilvert, 78352 Jouy en Josas Cedex, France
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  • Edited by A. Klier

Abstract

Genome plasticity is considered as a means for bacteria to adapt to their environment. Plasticity in tandem repeat sequences on bacterial genomes has been recently exploited to trace the epidemiology of pathogens. Here, we examine the utility of minisatellite (i.e., a repeat unit of six nucleotides or more) typing in non-pathogenic food bacteria of the species Lactococcus lactis. Thirty-four minisatellites identified on the sequenced L. lactis ssp. lactis strain IL1403 genome were first analyzed in 10 closely related ssp. lactis strains, as determined by randomly amplified polymorphic DNA (RAPD). The selected tandem repeats varied in length, percent identity between repeats, and locations. We showed that: (i) the greatest polymorphism was in orfs encoding exported proteins or in intergenic regions; (ii) two thirds of minisatellites were little- or non-variable, despite as much as 90% identity between tandem repeats; and (iii) dendrograms based on either RAPD or minisatellite analyses were similar. Seven minisatellites identified in this study are potentially useful for lactococcal typing. We then asked whether tandem repeats in L. lactis were stable upon very long-term (up to two years) storage. Despite large rearrangements previously reported in derivative strains, just one of 10 minisatellites tested underwent an alteration, suggesting that tandem repeat rearrangements probably occur during active DNA replication. We conclude that multiple locus minisatellite analysis can be a valuable tool to follow lactococcal strain diversity.

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