The Role of Transient Hypermutators in Adaptive Mutation in Escherichia coli

Microbial populations under nonlethal selection can give rise to mutations that relieve the selective pressure, a phenomenon that has come to be called "adaptive mutation." One explanation for adaptive mutation is that a small proportion of the cells experience a period of transient hyperm...

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Bibliographic Details
Published in:Proceedings of the National Academy of Sciences - PNAS 1999-06, Vol.96 (12), p.6862-6867
Main Authors: Rosche, William A., Foster, Patricia L., Cairns, John
Format: Article
Language:English
Subjects:
Alleles
Bacteria
Biological Sciences
Chromosomes
E coli
Escherichia coli
Escherichia coli - genetics
Gene Expression Regulation, Bacterial
Genetic mutation
Genetic screening
Genetics
Genome, Bacterial
Lac Operon
Molecular genetics
Mutation
Phenotypes
Plasmids
Population growth
Zero
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Summary:Microbial populations under nonlethal selection can give rise to mutations that relieve the selective pressure, a phenomenon that has come to be called "adaptive mutation." One explanation for adaptive mutation is that a small proportion of the cells experience a period of transient hypermutation, and that these hypermutators account for the mutations that appear. The experiments reported here investigated the contribution that hypermutators make to the mutations occurring in a Lac- strain of Escherichia coli during selection for lactose utilization. A broad mutational screen, loss of motility, was used to compare the frequency of nonselected mutations in starved Lac- cells, in Lac+ revertants, and in Lac+ revertants carrying yet another nonselected mutation. These frequencies allowed us to calculate that the hypermutating subpopulation makes up ≈ 0.06% of the population and that its mutation rate is elevated ≈ 200-fold. From these numbers we conclude that the hypermutators are responsible for nearly all multiple mutations but produce only ≈ 10% of the adaptive Lac+ mutations.
ISSN:0027-8424
1091-6490
DOI:10.1073/pnas.96.12.6862