The MG1363 and IL1403 Laboratory Strains of Lactococcus lactis and Several Dairy Strains Are Diploid

Ole Michelsen, Flemming G. Hansen, B. Albrechtsen, Peter Ruhdal Jensen

    Research output: Contribution to journalJournal articleResearchpeer-review

    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.
    Original languageEnglish
    JournalJournal of Bacteriology
    Volume192
    Issue number4
    Pages (from-to)1058-1065
    ISSN0021-9193
    DOIs
    Publication statusPublished - 2010

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