Center for Systems Microbiology, Department of System Biology, Technical University of Denmark, Lyngby, Denmark.
J Bacteriol. 2010 Feb;192(4):1058-65. doi: 10.1128/JB.00900-09. Epub 2009 Dec 18.
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.
细菌通常为单倍体,在一条环状染色体中保持一份基因组。我们检测了实验室培养的乳酸乳球菌的细胞周期,令我们惊讶的是,我们发现这些菌株中的一些生来就有两条完整的非复制染色体。我们通过流式细胞术和放射性标记 DNA 来确定细胞内的 DNA 含量。这些菌株因此符合二倍体的标准。我们还发现一些乳制品菌株也是二倍体,而一些非乳制品菌株和其他一些乳制品菌株在缓慢生长的培养物中是单倍体。二倍体和单倍体菌株在对紫外线的敏感性、细胞大小以及 DNA 复制终止和细胞分裂之间的 D 期方面存在差异。