Molecular evolution of bacterial pathogens
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.
Next: Dissertation Defense- Molecular systematics and biogeography of sexual and asexual forms of Poeciliopsis (Cyprinodontiformes- Poeciliidae)