title: 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.
authors.affiliation: Center for Systems Microbiology, Department of System Biology, Technical University of Denmark, Lyngby, Denmark. om@bio.dtu.dk
authors.forename: Ole
authors.initials: O
authors.lastname: Michelsen
authors.forename: Flemming G
authors.initials: FG
authors.lastname: Hansen
authors.forename: Bjarne
authors.initials: B
authors.lastname: Albrechtsen
authors.forename: Peter Ruhdal
authors.initials: PR
authors.lastname: Jensen
mesh_terms: D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial / Q000032:analysis; D004171:Diploidy; D005434:Flow Cytometry / Q000379:methods; D013294:Lactococcus lactis / Q000737:chemistry / Q000235:genetics* / Q000528:radiation effects; D011849:Radioactive Tracers; D013194:Staining and Labeling / Q000379:methods; D014466:Ultraviolet Rays
chemical_list: D004269:DNA, Bacterial; D011849:Radioactive Tracers