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Proc Natl Acad Sci U S A. 2005 Aug 23;102(34):12112-6. Epub 2005 Aug 12.

Bacterial genome size reduction by experimental evolution.

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1
Microbiology and Tumor Biology Center, Karolinska Institute, SE-171 77 Stockholm, Sweden.

Abstract

Bacterial evolution toward endosymbiosis with eukaryotic cells is associated with extensive bacterial genome reduction and loss of metabolic and regulatory capabilities. Here we examined the rate and process of genome reduction in the bacterium Salmonella enterica by a serial passage experimental evolution procedure. The initial rate of DNA loss was estimated to be 0.05 bp per chromosome per generation for a WT bacterium and approximately 50-fold higher for a mutS mutant defective in methyl-directed DNA mismatch repair. The endpoints were identified for seven chromosomal deletions isolated during serial passage and in two separate genetic selections. Deletions ranged in size from 1 to 202 kb, and most of them were not associated with DNA repeats, indicating that they were formed via RecA-independent recombination events. These results suggest that extensive genome reduction can occur on a short evolutionary time scale and that RecA-dependent homologous recombination only plays a limited role in this process of jettisoning superfluous DNA.

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PMID:
16099836
PMCID:
PMC1189319
DOI:
10.1073/pnas.0503654102
[Indexed for MEDLINE]
Free PMC Article
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