Abstract
BackgroundLactococcus lactis is among the most widely studied lactic acid bacterial species due to its long history of safe use and economic importance to the dairy industry, where it is exploited as a starter culture in cheese production.ResultsIn the current study, we report on the complete sequencing of 16 L. lactis subsp. lactis and L. lactis subsp. cremoris genomes. The chromosomal features of these 16 L. lactis strains in conjunction with 14 completely sequenced, publicly available lactococcal chromosomes were assessed with particular emphasis on discerning the L. lactis subspecies division, evolution and niche adaptation. The deduced pan-genome of L. lactis was found to be closed, indicating that the representative data sets employed for this analysis are sufficient to fully describe the genetic diversity of the taxon.ConclusionsNiche adaptation appears to play a significant role in governing the genetic content of each L. lactis subspecies, while (differential) genome decay and redundancy in the dairy niche is also highlighted.
Highlights
Lactococcus lactis is among the most widely studied lactic acid bacterial species due to its long history of safe use and economic importance to the dairy industry, where it is exploited as a starter culture in cheese production
General genome features In this study, the chromosomal features of 30 L. lactis strains were assessed, 18 of which belong to subspecies lactis and a further 12 to subspecies cremoris based on phylogenetic analysis of 16S RNA
The 30 L. lactis strains included in this study encompass six different ecological niches; dairy, plant, meat, fermented foods, human isolate and a strain isolated from a sink drain, with the vast majority isolated from the dairy environment, most notably for the production of cheese (Table 1)
Summary
Lactococcus lactis is among the most widely studied lactic acid bacterial species due to its long history of safe use and economic importance to the dairy industry, where it is exploited as a starter culture in cheese production. Lactococcal strains are important to the dairy industry, where they are employed as starter cultures for cheese production. Reductive evolution and genome decay have previously been reported in ‘domesticated’, dairy L. lactis strains, those belonging to subspecies cremoris [6, 7]. Niche adaptation by lactococcal strains has been investigated most thoroughly in relation to the dairy environment In this particular niche, strain adaptations appear to be mainly plasmid-encoded and two examples of this are lactose and citrate utilisation. The classification of Cit+ lactococci as L. lactis subsp. lactis biovar diacetylactis has led to confusion as plasmid-encoded characteristics can be transferred from one strain to another and may lead to incorrect
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