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Appl. Environ. Microbiol. doi:10.1128/AEM.01253-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

EVOLUTIONARY DYNAMICS OF RALSTONIA SOLANACEARUM

Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, Illinois 60637, USA; PROINPA Foundation, Cochabamba, Bolivia

^* To whom correspondence should be addressed. Email: jgreenbe{at}midway.uchicago.edu.

	Abstract

We investigated the genetic diversity, extent of recombination, natural selection and population divergence of worldwide Ralstonia solanacearum samples. This plant pathogen causes bacterial wilt in many crops and constitutes a serious threat to agricultural production due to its very wide host range and aggressiveness. Five housekeeping genes, dispersed around the chromosome, and three virulence-related genes, located on the megaplasmid, were sequenced from 58 strains belonging to the four major phylogenetic clusters (phylotypes). Whereas genetic variation is high and consistent for all housekeeping loci studied, virulence-related gene sequences are more diverse. Phylogenetic and statistical analyses suggest that this organism is a highly diverse bacterial species, containing four major, deeply separated evolutionary lineages (phylotypes I to IV) as well as a weaker subdivision of phylotype II into two subgroups. The analysis of molecular variation showed that the geographic isolation and spatial distance have been the significant determinants of genetic variation between phylotypes. R. solanacearum displays high clonality for housekeeping genes in all phylotypes (except phylotype III) and significant levels of recombination for the virulence-related egl and hrpB genes, which is limited mainly to phylotype III and IV strains. Finally, genes essential for species survival are under purifying selection and those directly involved in pathogenesis might be under diversifying selection.

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