School of Life Sciences, Central China Normal University, Wuhan, China
mSphere. 2018 Oct 24;3(5):e00430-18. doi: 10.1128/mSphere.00430-18.
Bacterial cell size is closely associated with biomass growth and cell cycle progression, including chromosome replication and cell division. It is generally proposed that cells tightly control the timing of chromosome replication through maintaining a constant cell volume per origin upon initiating chromosome replication (constant initiation volume) under various growth conditions. Here, we quantitatively characterize the cell size and cell cycle of cells growing exponentially under hyperosmotic stress, which is a common environmental stressor that profoundly affects the bacterial water content. The bacterial cell size is reduced by hyperosmotic stress, even though the C and D periods are remarkably prolonged, indicating a significantly reduced initiation volume. The reduced initiation volume originates from the higher concentration of DnaA initiator protein caused by water loss at high osmolarity. Our study shows suggests a fundamental role of water content in regulating bacterial cell size and has also revealed a new role of the DnaA protein in regulating the chromosome replication elongation beyond regulating the replication initiation process. Bacterial cell size depends on growth rate, cell cycle progression, and the cell volume per origin upon initiating chromosome replication (initiation volume). Here, we perform the first systematic and quantitative study of the effect of hyperosmotic stress on the cell size and cell cycle. We find that hyperosmotic stress significantly reduces the initiation volume. The reduced initiation volume is attributed to the increased DnaA concentration caused by water loss at high osmolarity, indicating a fundamental role of water content in cell size and cell cycle regulation.
细菌细胞大小与生物量生长和细胞周期进程密切相关，包括染色体复制和细胞分裂。通常认为，细胞通过在各种生长条件下起始染色体复制时保持每个起始点的恒定细胞体积（恒定起始体积），来紧密控制染色体复制的时间。在这里，我们定量表征了在高渗胁迫下指数生长的 细胞的细胞大小和细胞周期，高渗胁迫是一种常见的环境胁迫因子，会深刻影响细菌的含水量。尽管 C 和 D 期显著延长，细菌细胞大小仍因高渗胁迫而减小，表明起始体积显著减小。起始体积的减小源于高渗透压下水分流失导致的 DnaA 起始蛋白浓度升高。我们的研究表明，含水量在调节细菌细胞大小方面起着基础性作用，同时也揭示了 DnaA 蛋白在调节染色体复制延伸过程中的一个新作用，超越了其在调节复制起始过程中的作用。细菌细胞大小取决于生长速率、细胞周期进程以及起始染色体复制时的每个起始点的细胞体积（起始体积）。在这里，我们首次对高渗胁迫对 细胞大小和细胞周期的影响进行了系统和定量的研究。我们发现高渗胁迫显著降低了起始体积。起始体积的减小归因于高渗透压下水分流失导致的 DnaA 浓度升高，表明含水量在细胞大小和细胞周期调控中起着基础性作用。
