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The lactic acid bacterium Lactococcus lactis is widely used for the production of fermented dairy products. Here, we present the draft genome sequences of 24 L. lactis strains isolated from different environments and geographic locations.
Lactococcus lactis is a Gram-positive bacterium that is predominantly found on plant material and in the dairy environment (1, 2). It is extensively used in dairy fermentations (3), which is mainly due to its role in the development of texture and flavor through, e.g., proteolysis and the production of volatile flavor compounds (4). It also contributes to food preservation through the production of organic acids and bacteriocins such as nisin (5). Four L. lactis subspecies have been defined (6): subsp. lactis (7), subsp. cremoris (8), subsp. hordniae (9), and subsp. tructae (10). In this study we report the draft genome sequences of 24 L. lactis strains, of which 23 belong to subspecies lactis and one (LMG8520) is the type strain for the subspecies hordniae (Table 1) (11). However, we found in a detailed phylogenetic and comparative genome analysis that strain LMG8520 has a L. lactis subsp. lactis genotype.
The strains were grown overnight in 5 mL LM17 broth at 30°C. After propagation in fresh medium, cells were harvested during midexponential growth and total DNA was isolated as previously described (11) with the following modifications. Cell pellets were resuspended in a buffer [6.7% sucrose, 1 mM EDTA, 50 Mm TrisHCl (pH 8.0)] and incubated with RNase (0.5 mg/mL) and lysozyme (2 mg/mL) at 37°C for 1 h. Subsequently, cells were lysed by treating the samples with SDS (1% wt/vol final concentration) at 37°C for 10 min. The total DNA was extracted with phenol-chloroform, precipitated with isopropanol and sodium acetate (12), and dissolved in sterile water.
Whole-genome sequencing was performed at GATC Biotech (Konstanz, Germany) with 50 bp paired-end libraries on an Illumina HiSeq 2000. Raw sequence reads of each of the genomes were assembled de novo using IDBA (13) with default parameters at a target coverage of 50×. This resulted in draft genomic sequences for 24 L. lactis strains (Table 1). Annotation of the contig sequences was performed by the RAST server (14).
The genome sequences of the 24 L. lactis strains have been deposited as whole-genome shotgun projects at DDBJ/EMBL/GenBank under the accession numbers listed in Table 1.
Citation Backus L, Wels M, Boekhorst J, Dijkstra AR, Beerthuyzen M, Kelly WJ, Siezen RJ, van Hijum SAFT, Bachmann H. 2017. Draft genome sequences of 24 Lactococcus lactis strains. Genome Announc 5:e01737-16. https://doi.org/10.1128/genomeA.01737-16.