Department of Molecular and Cellular Biology, Howard Hughes Medical Institute, Harvard Faculty of Arts and Sciences Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2012 Aug 21;109(34):13638-43. doi: 10.1073/pnas.1211144109. Epub 2012 Aug 6.
Many cyanobacteria have been shown to harbor multiple chromosome copies per cell, yet little is known about the organization, replication, and segregation of these chromosomes. Here, we visualize individual chromosomes in the cyanobacterium Synechococcus elongatus via time-lapse fluorescence microscopy. We find that chromosomes are equally spaced along the long axis of the cell and are interspersed with another regularly spaced subcellular compartment, the carboxysome. This remarkable organization of the cytoplasm along with accurate midcell septum placement allows for near-optimal segregation of chromosomes to daughter cells. Disruption of either chromosome ordering or midcell septum placement significantly increases the chromosome partitioning error. We find that chromosome replication is both asynchronous and independent of the position of the chromosome in the cell and that spatial organization is preserved after replication. Our findings on chromosome organization, replication, and segregation in S. elongatus provide a basis for understanding chromosome dynamics in bacteria with multiple chromosomes.
许多蓝藻每个细胞中都含有多个染色体拷贝，但对于这些染色体的组织、复制和分离知之甚少。在这里，我们通过延时荧光显微镜观察到了蓝藻聚球藻（Synechococcus elongatus）中的单个染色体。我们发现染色体沿细胞长轴等距排列，与另一个规则间隔的亚细胞区室——羧基体交错排列。这种细胞质的显著组织方式以及准确的细胞中部隔膜的位置，使得染色体能够近乎最优地分配到子细胞中。染色体排序或细胞中部隔膜位置的任何破坏都会显著增加染色体分配错误。我们发现，染色体的复制既不同步，也与染色体在细胞中的位置无关，并且在复制后空间组织得以保留。我们在聚球藻中的染色体组织、复制和分离方面的发现为理解具有多个染色体的细菌中的染色体动力学提供了基础。
