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Directed evolution of cell size in Escherichia coli.

Yoshida M, Tsuru S, Hirata N, Seno S, Matsuda H, Ying BW, Yomo T - BMC Evol. Biol. (2014)

Bottom Line: This selection-propagation cycle was repeated, and significant changes in cell size were detected within 400 generations.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.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. maaaaaari8852@gmail.com.

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.

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Related in: MedlinePlus

Evolution process and final populations of evolved lineages. The trajectory of the cell concentration (A), the mean cell size (B) and the standard deviation (C) under the size selection process. Open diamond, open circle and closed circle represent the Svr-, Mld- and T-lineages, respectively. (D) Cell size distributions of the population of the final round (left) and the isolated 12 clones (right), where the isolates are distinguished by gray-scaled lines. The top two panels represent ancestral clones. The other panels correspond to the T-, Svr- and Mld- lineages at the bottom. The insets represent the Cell IDs in Table 1. All data were obtained at approximately 107 cells/ml. The dotted line indicates one of the AC isolated clones (top left). (E) Phase contrast images of the isolated clones are shown. The insets also represent the Cell IDs in Table 1. The white bars indicate 10 μm. (F) The mean cell size of the 12 isolates. (G) The standard deviation in cell size of the 12 isolates. The error bars are 95% confidence limits. P-values are for t-test (N = 12).
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Fig3: Evolution process and final populations of evolved lineages. The trajectory of the cell concentration (A), the mean cell size (B) and the standard deviation (C) under the size selection process. Open diamond, open circle and closed circle represent the Svr-, Mld- and T-lineages, respectively. (D) Cell size distributions of the population of the final round (left) and the isolated 12 clones (right), where the isolates are distinguished by gray-scaled lines. The top two panels represent ancestral clones. The other panels correspond to the T-, Svr- and Mld- lineages at the bottom. The insets represent the Cell IDs in Table 1. All data were obtained at approximately 107 cells/ml. The dotted line indicates one of the AC isolated clones (top left). (E) Phase contrast images of the isolated clones are shown. The insets also represent the Cell IDs in Table 1. The white bars indicate 10 μm. (F) The mean cell size of the 12 isolates. (G) The standard deviation in cell size of the 12 isolates. The error bars are 95% confidence limits. P-values are for t-test (N = 12).

Mentions: Starting from a genetically identical cell population of BSKY, we tested the possibility of evolution toward a smaller cell size through size selections, where the strength of the selection was examined in 2 ways (Figure 2A and B). Our experimental rounds consist of two simple selections, size selection via FACS and growth selection in a culture. The cells whose size met the selection criteria represented greater fitness in the size selection, and faster-growing cells naturally outcompeted slow-growing cells in the cultures. The cells were sampled from the overnight culture, and the particular fractions exhibiting the target sizes were sorted to fresh medium using FACS. The size selections were examined in the smallest 1% of the cells (severe selection) and around the peak (mild selection) to yield the Svr- and Mld-lineages, respectively. The numbers of the sorted cells were decided based on the growth rate of the previous round, so they reached approximately 107 cells/ml after overnight culturing. The typical values were 20 to 2000 cells in 1 ml of fresh medium. Consistent with the small population sizes, the cell concentrations fluctuated day by day, even in the general serial transfer cells (T-lineage) (Figure 3A). These rounds were repeated daily, in parallel with the T-lineage, which was not sorted by size using FACS and used as a control (Figure 2C). More detailed procedures are described in the Methods section.Figure 2


Directed evolution of cell size in Escherichia coli.

Yoshida M, Tsuru S, Hirata N, Seno S, Matsuda H, Ying BW, Yomo T - BMC Evol. Biol. (2014)

Evolution process and final populations of evolved lineages. The trajectory of the cell concentration (A), the mean cell size (B) and the standard deviation (C) under the size selection process. Open diamond, open circle and closed circle represent the Svr-, Mld- and T-lineages, respectively. (D) Cell size distributions of the population of the final round (left) and the isolated 12 clones (right), where the isolates are distinguished by gray-scaled lines. The top two panels represent ancestral clones. The other panels correspond to the T-, Svr- and Mld- lineages at the bottom. The insets represent the Cell IDs in Table 1. All data were obtained at approximately 107 cells/ml. The dotted line indicates one of the AC isolated clones (top left). (E) Phase contrast images of the isolated clones are shown. The insets also represent the Cell IDs in Table 1. The white bars indicate 10 μm. (F) The mean cell size of the 12 isolates. (G) The standard deviation in cell size of the 12 isolates. The error bars are 95% confidence limits. P-values are for t-test (N = 12).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4279887&req=5

Fig3: Evolution process and final populations of evolved lineages. The trajectory of the cell concentration (A), the mean cell size (B) and the standard deviation (C) under the size selection process. Open diamond, open circle and closed circle represent the Svr-, Mld- and T-lineages, respectively. (D) Cell size distributions of the population of the final round (left) and the isolated 12 clones (right), where the isolates are distinguished by gray-scaled lines. The top two panels represent ancestral clones. The other panels correspond to the T-, Svr- and Mld- lineages at the bottom. The insets represent the Cell IDs in Table 1. All data were obtained at approximately 107 cells/ml. The dotted line indicates one of the AC isolated clones (top left). (E) Phase contrast images of the isolated clones are shown. The insets also represent the Cell IDs in Table 1. The white bars indicate 10 μm. (F) The mean cell size of the 12 isolates. (G) The standard deviation in cell size of the 12 isolates. The error bars are 95% confidence limits. P-values are for t-test (N = 12).
Mentions: Starting from a genetically identical cell population of BSKY, we tested the possibility of evolution toward a smaller cell size through size selections, where the strength of the selection was examined in 2 ways (Figure 2A and B). Our experimental rounds consist of two simple selections, size selection via FACS and growth selection in a culture. The cells whose size met the selection criteria represented greater fitness in the size selection, and faster-growing cells naturally outcompeted slow-growing cells in the cultures. The cells were sampled from the overnight culture, and the particular fractions exhibiting the target sizes were sorted to fresh medium using FACS. The size selections were examined in the smallest 1% of the cells (severe selection) and around the peak (mild selection) to yield the Svr- and Mld-lineages, respectively. The numbers of the sorted cells were decided based on the growth rate of the previous round, so they reached approximately 107 cells/ml after overnight culturing. The typical values were 20 to 2000 cells in 1 ml of fresh medium. Consistent with the small population sizes, the cell concentrations fluctuated day by day, even in the general serial transfer cells (T-lineage) (Figure 3A). These rounds were repeated daily, in parallel with the T-lineage, which was not sorted by size using FACS and used as a control (Figure 2C). More detailed procedures are described in the Methods section.Figure 2

Bottom Line: This selection-propagation cycle was repeated, and significant changes in cell size were detected within 400 generations.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.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Information Science and Technology, Osaka University, 1-5 Yamadaoka, Suita, Osaka, 565-0871, Japan. maaaaaari8852@gmail.com.

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.

Show MeSH
Related in: MedlinePlus