Sex and virulence in Escherichia coli: an evolutionary perspective

TLDR: The evolution of virulence is linked to bacterial sex because rates of evolution have accelerated in pathogenic lineages, culminating in highly virulent organisms whose genomic contents are altered frequently by increased rates of homologous recombination.

Abstract: Summary Pathogenic Escherichia coli cause over 160 million cases of dysentery and one million deaths per year, whereas non-pathogenic E. coli constitute part of the normal intestinal flora of healthy mammals and birds. The evolutionary pathways underlying this dichotomy in bacterial lifestyle were investigated by multilocus sequence typing of a global collection of isolates. Specific pathogen types (enterohaemorrhagic E. coli , enteropathogenic E. coli , enteroinvasive E. coli , K1 and Shigella ) have arisen independently and repeat- edly in several lineages, whereas other lineages con- tain only few pathogens. Rates of evolution have accelerated in pathogenic lineages, culminating in highly virulent organisms whose genomic contents are altered frequently by increased rates of homolo- gous recombination; thus, the evolution of virulence is linked to bacterial sex. This long-term pattern of evolution was observed in genes distributed through- out the genome, and thereby is the likely result of episodic selection for strains that can escape the host immune response.