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The MG1363 and IL1403 laboratory strains of Lactococcus lactis and several dairy strains are diploid.

ABSTRACT: Bacteria are normally haploid, maintaining one copy of their genome in one circular chromosome. We have examined the cell cycle of laboratory strains of Lactococcus lactis, and, to our surprise, we found that some of these strains were born with two complete nonreplicating chromosomes. We determined the cellular content of DNA by flow cytometry and by radioactive labeling of the DNA. These strains thus fulfill the criterion of being diploid. Several dairy strains were also found to be diploid while a nondairy strain and several other dairy strains were haploid in slow-growing culture. The diploid and haploid strains differed in their sensitivity toward UV light, in their cell size, and in their D period, the period between termination of DNA replication and cell division.

SUBMITTER: Michelsen O

PROVIDER: S-EPMC2812979 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Recently, we demonstrated that fermentation conditions strongly impact on subsequent survival of Lactococcus lactis strain MG1363 during heat and oxidative stress, two important parameters during spray drying. Moreover, employment of a transcriptome-phenotype matching approach revealed groups of genes associated with robustness towards heat and/or oxidative stress. To investigate if other strains have similar or distinct transcriptome signatures for robustness, we applied a similar transcriptome-robustness phenotype matching approach on the L. lactis strains IL1403, KF147 and SK11. These strains were employed in an identical fermentation regime as was performed earlier for strain MG1363 which consisted of twelve conditions, varying in the presence of salt and/or oxygen, as well as fermentation temperature and pH. In the exponential phase of growth, cells were harvested for transcriptome analysis and assessment of heat and oxidative stress survival phenotypes. The variation in fermentation conditions resulted in differences in heat and oxidative stress survival up to five 10-log units. Effects of the fermentation conditions on stress survival of the L. lactis strains were typically strain-dependent, although the fermentation conditions had mainly similar effects on the growth characteristics of the different strains. Association of transcriptomes and robustness phenotypes identified highly strain-specific transcriptome signatures for robustness, indicating that multiple mechanism exist to increase robustness and, as a consequence, robustness of each strain requires individual optimization. However, a relatively small overlap in the transcriptome responses of the strains was also identified and this generic transcriptome signature included genes previously associated with stress (ctsR and lplL) and novel genes, including nanE and genes encoding transport proteins. The transcript levels of these genes can function as indicators of robustness and could aid in selection of fermentation parameters, potentially resulting in more optimal robustness during spray drying.

Dataset Information

The MG1363 and IL1403 laboratory strains of Lactococcus lactis and several dairy strains are diploid.

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