Enhancing effect of phenotype mutational robustness on adaptation in Escherichia coli

Theoretical and computational studies predict a positive role for widespread phenotype resistance to genetic mutation, or "phenotype mutational robustness," in enhancing adaptation to novel environments through the accumulation of cryptic genetic variation. However, this has not been verified through experimental evolution in biological systems at the level of whole organisms. In a short-term evolution experiment of about 250 generations, we studied the adaptive performances of independently evolving populations of the bacterium Escherichia coli in two new nutritional environments, represented by minimal media with either lactate or glycerol as the sole carbon source. At the start of the experiments, all populations expressed identical phenotype, while differing for the amount of cryptic genetic variation, artificially produced by mutagenesis. We found that cryptic genetic variation can promote significantly faster adaptation to a new nutritional environment in E. coli. The scale of this effect varies between the two environments, and correlates with an estimation of the phenotype robustness of the ability to grow in a given medium, based on survival rate after mutagenesis in the same medium.