Affiliation:
1. Molecular Biology Branch, Center for Food Safety & Applied Nutrition, Food and Drug Administration, Washington, D.C. 20204
Abstract
ABSTRACT
mutS
mutators accelerate the bacterial mutation rate 100- to 1,000-fold and relax the barriers that normally restrict homeologous recombination. These mutators thus afford the opportunity for horizontal exchange of DNA between disparate strains. While much is known regarding the
mutS
phenotype, the evolutionary structure of the
mutS
+
gene in
Escherichia coli
remains unclear. The physical proximity of
mutS
to an adjacent polymorphic region of the chromosome suggests that this gene itself may be subject to horizontal transfer and recombination events. To test this notion, a phylogenetic approach was employed that compared gene phylogeny to strain phylogeny, making it possible to identify
E. coli
strains in which
mutS
alleles have recombined. Comparison of
mutS
phylogeny against predicted
E. coli
“whole-chromosome” phylogenies (derived from multilocus enzyme electrophoresis and
mdh
sequences) revealed striking levels of phylogenetic discordance among
mutS
alleles and their respective strains. We interpret these incongruences as signatures of horizontal exchange among
mutS
alleles. Examination of additional sites surrounding
mutS
also revealed incongruous distributions compared to
E. coli
strain phylogeny. This suggests that other regional sequences are equally subject to horizontal transfer, supporting the hypothesis that the 61.5-min
mutS-rpoS
region is a recombinational hot spot within the
E. coli
chromosome. Furthermore, these data are consistent with a mechanism for stabilizing adaptive changes promoted by
mutS
mutators through rescue of defective
mutS
alleles with wild-type sequences.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
60 articles.
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