Adaptive Mutations in Bacteria: High Rate and Small Effects

  title={Adaptive Mutations in Bacteria: High Rate and Small Effects},
  author={L{\'i}lia Perfeito and Lisete Fernandes and Catarina Mota and Isabel Gordo},
  pages={813 - 815}
Evolution by natural selection is driven by the continuous generation of adaptive mutations. We measured the genomic mutation rate that generates beneficial mutations and their effects on fitness in Escherichia coli under conditions in which the effect of competition between lineages carrying different beneficial mutations is minimized. We found a rate on the order of 10–5 per genome per generation, which is 1000 times as high as previous estimates, and a mean selective advantage of 1%. Such a… 
Rate of fixation of beneficial mutations in sexual populations.
Simulation results demonstrate that evidence of clonal interference, as increased mean selective effect of fixed mutations and reduced likelihood of fixation of small-effect mutations, are also present in sexual populations, although this evidence is delayed when compared to asexual populations.
Fitness Effects of Mutations in Bacteria
Some of the important findings of mutation effects in bacteria revealed through laboratory experiments are reviewed.
Mutation, Selection and Genetic Interactions in Bacteria
Experimental evolution with bacteria presents the opportunity to directly measure the rate at which new mutations typically occur, their effects on fitness and the strength and type of genetic interactions between different mutations, which are key for understanding the evolution of any population.
The First Steps of Adaptation of Escherichia coli to the Gut Are Dominated by Soft Sweeps
The intense clonal interference during adaptation to the gut environment, here demonstrated, may be important for the understanding of the levels of strain diversity of E. coli inhabiting the human gut microbiota and of its recombination rate.
Fitness Is Strongly Influenced by Rare Mutations of Large Effect in a Microbial Mutation Accumulation Experiment
A classic MA experiment in which frequent sampling of MA lines was combined with whole genome resequencing to develop a high-resolution picture of the effect of spontaneous mutations in a hypermutator strain of the bacterium Pseudomonas aeruginosa found that average fitness across all lines decayed linearly over time.
Rate and effects of spontaneous mutations that affect fitness in mutator Escherichia coli
The rate and mean effect of spontaneous mutations that affect fitness in a mutator strain of Escherichia coli are estimated and some of the estimation methods associated with mutation accumulation (MA) experiments are reviewed.
Genome evolution and adaptation in a long-term experiment with Escherichia coli
Although adaptation decelerated sharply, genomic evolution was nearly constant for 20,000 generations, which is usually viewed as the signature of neutral evolution, but several lines of evidence indicate that almost all of these mutations were beneficial.
Diminishing Returns From Beneficial Mutations and Pervasive Epistasis Shape the Fitness Landscape for Rifampicin Resistance in Pseudomonas aeruginosa
It is argued that a simple overall pattern of diminishing-returns adaptation emerges, despite pervasive epistasis between beneficial mutations, because many beneficial mutations are available, and while the fitness landscape is rugged at the fine scale, it is smooth and regular when the authors consider the average over possible routes to adaptation.
The role of clonal interference across genetic backgrounds and environments
It is shown that effective parameters will not always reflect the rate and mean effect of beneficial mutations, especially when the distribution of arising mutations has high variance, and the mutation rate is high.


Fitness effects of advantageous mutations in evolving Escherichia coli populations.
  • M. Imhof, C. Schlotterer
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 2001
A novel marker system is used to trace adaptive events in an evolving Escherichia coli culture and to determine the selective advantage of those beneficial mutations and to estimate the rate of beneficial mutations to be 4 x 10(-9) per cell and generation.
The rate of adaptive evolution in enteric bacteria.
It is shown that the proportion of adaptive substitutions is uncorrelated with the rate of amino acid substitution or gene function but that it may be correlated with levels of synonymous codon usage bias.
Mutations of intermediate effect are responsible for adaptation in evolving Pseudomonas fluorescens populations
This experiment suggests that the initial stages of adaptation to stressful environments will involve the substitution of mutations with large effect on fitness, possibly because the ancestral population grows poorly in serine-limited medium.
Distribution of fitness effects among beneficial mutations before selection in experimental populations of bacteria
The results suggest that the initial step in adaptive evolution—the production of novel beneficial mutants from which selection sorts—is very general, being characterized by an approximately exponential distribution with many mutations of small effect and few of large effect.
Estimation of spontaneous genome-wide mutation rate parameters: whither beneficial mutations?
It is argued that, although most if not all mutations detected in mutation accumulation experiments are deleterious, the question of the rate of favourable mutations (and their effects) is still a matter for debate.
An Equivalence Principle for the Incorporation of Favorable Mutations in Asexual Populations
It is demonstrated that evolution in asexual populations is driven by the fitness effects and appearance times of only a small minority of favorable mutations, and much of the evolutionary dynamics can be encapsulated in two parameters—an effective selection coefficient and effective rate of beneficial mutations.
Spontaneous Mutations in Diploid Saccharomyces cerevisiae
A major mutation-accumulation experiment in the yeast, Saccharomyces cerevisiae, found that 5.75% of the fitness-altering mutations accumulated were beneficial, contradicting the widely held belief that nearly all fitness- altering mutations are deleterious.
The Number of Mutations Selected During Adaptation in a Laboratory Population of Saccharomyces cerevisiae
I studied the genetics of adaptation by populations of budding yeast to a culture regime of daily hundredfold dilution and transfer in a glucose-limited minimal liquid medium and indicated that deleterious mutations had hitchhiked with adaptive mutations in this evolved genotype.