Journal Article

Chromosomal Diversity in <i>Lactococcus lactis</i> and the Origin of Dairy Starter Cultures

William J. Kelly, Lawrence J. H. Ward and Sinead C. Leahy

in Genome Biology and Evolution

Published on behalf of Society for Molecular Biology and Evolution

Volume 2, issue , pages 729-744
Published in print January 2010 |
Published online August 2010 | e-ISSN: 1759-6653 | DOI:

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  • Bioinformatics and Computational Biology
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A large collection of Lactococcus lactis strains, including wild-type isolates and dairy starter cultures, were screened on the basis of their phenotype and the macrorestriction patterns produced from pulsed-field gel electrophoresis (PFGE) analysis of SmaI digests of genomic DNA. Three groups of dairy starter cultures, used for different purposes in the dairy industry, and a fourth group made up of strains isolated from the environment were selected for analysis of their chromosomal diversity using the endonuclease I-CeuI. Chromosome architecture was largely conserved with each strain having six copies of the rRNA genes, and the chromosome size of individual strains ranged between 2,240 and 2,688 kb. The origin of L. lactis strains showed the greatest correlation with chromosome size, and dairy strains, particularly those with the cremoris phenotype, had smaller chromosomes than wild-type strains. Overall, this study, coupled with analysis of the sequenced L. lactis genomes, provides evidence that defined strain dairy starter cultures have arisen from plant L. lactis strains. Adaptation of these strains to the dairy environment has involved loss of functions resulting in smaller chromosomes and acquisition of genes (usually plasmid associated) that facilitate growth in milk. We conclude that dairy starter cultures generally and the industrially used cremoris and diacetylactis phenotype strains in particular comprise a specialized group of L. lactis strains that have been selected to become an essential component of industrial processes and have evolved accordingly, so that they are no longer fit to survive outside the dairy environment.

Keywords: L. lactis subsp. cremoris; L. lactis subsp. lactis; L. lactis subsp. lactis biovar diacetylactis; dairy starter cultures; PFGE; chromosome size

Journal Article.  8106 words.  Illustrated.

Subjects: Bioinformatics and Computational Biology ; Evolutionary Biology ; Genetics and Genomics

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