Cumulative number of cell divisions as a meaningful timescale for adaptive laboratory evolution of Escherichia coli

PLoS One. 2011;6(10):e26172. doi: 10.1371/journal.pone.0026172. Epub 2011 Oct 18.

Abstract

Adaptive laboratory evolution (ALE) under controlled conditions has become a valuable approach for the study of the genetic and biochemical basis for microbial adaptation under a given selection pressure. Conventionally, the timescale in ALE experiments has been set in terms of number of generations. As mutations are believed to occur primarily during cell division in growing cultures, the cumulative number of cell divisions (CCD) would be an alternative way to set the timescale for ALE. Here we show that in short-term ALE (up to 40-50 days), Escherichia coli, under growth rate selection pressure, was found to undergo approximately 10(11.2) total cumulative cell divisions in the population to produce a new stable growth phenotype that results from 2 to 8 mutations. Continuous exposure to a low level of the mutagen N-methyl-N'-nitro-N-nitrosoguanidine was found to accelerate this timescale and led to a superior growth rate phenotype with a much larger number of mutations as determined with whole-genome sequencing. These results would be useful for the fundamental kinetics of the ALE process in designing ALE experiments and provide a basis for its quantitative description.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adaptation, Physiological / drug effects
  • Adaptation, Physiological / genetics*
  • Cell Division / drug effects
  • Cell Division / genetics*
  • Directed Molecular Evolution / methods*
  • Escherichia coli / cytology*
  • Escherichia coli / drug effects
  • Escherichia coli / genetics*
  • Escherichia coli / physiology
  • Genotype
  • Laboratories*
  • Methylnitronitrosoguanidine / pharmacology
  • Mutagens / pharmacology
  • Phenotype
  • Time Factors

Substances

  • Mutagens
  • Methylnitronitrosoguanidine