title: Directed evolution of cell size in Escherichia coli.
abstract: BACKGROUND
  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?
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. maaaaaari8852@gmail.com.
authors.forename: Mari
authors.initials: M
authors.lastname: Yoshida
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. tsuru_saburo@bio.eng.osaka-u.ac.jp.
authors.forename: Saburo
authors.initials: S
authors.lastname: Tsuru
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. naoko.h.1002@gmail.com.
authors.forename: Naoko
authors.initials: N
authors.lastname: Hirata
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. senoo@ist.osaka-u.ac.jp.
authors.forename: Shigeto
authors.initials: S
authors.lastname: Seno
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. matsuda@ist.osaka-u.ac.jp.
authors.forename: Hideo
authors.initials: H
authors.lastname: Matsuda
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8572, Japan. ying.beiwen.gf@u.tsukuba.ac.jp.
authors.forename: Bei-Wen
authors.initials: BW
authors.lastname: Ying
authors.affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. yomo@ist.osaka-u.ac.jp.|Graduate School of Frontier Biosciences, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. yomo@ist.osaka-u.ac.jp.|Exploratory Research for Advanced Technology (ERATO), Japan Science and Technology Agency (JST), Suita, Osaka, 565-0871, Japan. yomo@ist.osaka-u.ac.jp.|Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1-IE-1 Ookayama, Meguro-ku, Tokyo, 152-8550, Japan. yomo@ist.osaka-u.ac.jp.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yomo
mesh_terms: D005075:Biological Evolution; D019020:Directed Molecular Evolution; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics* / Q000254:growth & development; D005434:Flow Cytometry; D009154:Mutation; D012641:Selection, Genetic