Thomas S. Whittam
Michigan State University

Wednesday, April 3, 2002
3:00 p.m.–Pacific Forum

The introgression of new genes by horizontal transfer has played a major role in the adaptation and ecological specialization of bacterial lineages. For example Lawrence and Ochman (1999) estimate that as much as 18% of the current genome of Escherichia coli K-12 represents foreign DNA acquired since the divergence of E. coli and Salmonella enterica. Gene acquisitions have also contributed to the variation in virulence among pathogenic strains and closely related bacterial species. In some bacterial species, blocks of virulence genes, called pathogenicity islands, have been acquired at different times, thus generating a variety of pathogens with distinct virulence genes and mechanisms of pathogenesis. I will discuss evidence for the role of gene acquisition in the evolution and diversification of groups of pathogenic E. coli, including E. coli O157:H7, a foodborne pathogen and growing public health problem. In addition to the horizontal spread of virulence factors, I will present results of an ongoing investigation into the role of natural selection for acid tolerance and other aspects of durability in the external environment based on an experimental system of bacterial evolution.