Yoshida Mari, Tsuru Saburo, Hirata Naoko, Seno Shigeto, Matsuda Hideo, Ying Bei-Wen, Yomo Tetsuya
Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan.
BMC Evol Biol. 2014 Dec 17;14:257. doi: 10.1186/s12862-014-0257-1.
In bacteria, cell size affects chromosome replication, the assembly of division machinery, cell wall synthesis, membrane synthesis and ultimately growth rate. In addition, cell size can also be a target for Darwinian evolution for protection from predators. This strong coupling of cell size and growth, however, could lead to the introduction of growth defects after size evolution. An important question remains: can bacterial cell size change and/or evolve without imposing a growth burden?
The directed evolution of particular cell sizes, without a growth burden, was tested with a laboratory Escherichia coli strain. Cells of defined size ranges were collected by a cell sorter and were subsequently cultured. This selection-propagation cycle was repeated, and significant changes in cell size were detected within 400 generations. In addition, the width of the size distribution was altered. The changes in cell size were unaccompanied by a growth burden. Whole genome sequencing revealed that only a few mutations in genes related to membrane synthesis conferred the size evolution.
In conclusion, bacterial cell size could evolve, through a few mutations, without growth reduction. The size evolution without growth reduction suggests a rapid evolutionary change to diverse cell sizes in bacterial survival strategies.
在细菌中，细胞大小会影响染色体复制、分裂机器的组装、细胞壁合成、膜合成以及最终的生长速率。此外，细胞大小也可能成为达尔文式进化的目标，以抵御捕食者。然而，细胞大小与生长之间的这种紧密联系，可能会在大小进化后导致生长缺陷的出现。一个重要的问题仍然存在：细菌细胞大小能否在不带来生长负担的情况下发生变化和/或进化？
使用实验室大肠杆菌菌株对特定细胞大小在无生长负担情况下的定向进化进行了测试。通过细胞分选仪收集特定大小范围的细胞，随后进行培养。重复这个选择-繁殖循环，在400代内检测到细胞大小有显著变化。此外，大小分布的宽度也发生了改变。细胞大小的变化并未伴随着生长负担。全基因组测序显示，只有少数与膜合成相关的基因突变导致了大小进化。
总之，细菌细胞大小可以通过少数基因突变而进化，且不会降低生长速度。不降低生长速度的大小进化表明，细菌生存策略中向多种细胞大小的快速进化变化。
