Evolution of Shigella

There is a recently discovered strain of Escherichia coli that is frequently responsible for elevated bacterial (coliform) counts in Lake Burley Griffin and other ACT lakes and that also causes elevated counts in water reservoirs in NSW and QLD. This strain is significant not only because it can cause massively elevated coliform counts, but also because it has been known to circumvent water treatment measures and appear in drinking water distribution systems. The available evidence suggests that, unlike most E. coli, this strain is capable of persisting in the external environment in the absence of vertebrate faecal inputs. That is, it may be best considered as a free-living organism.

The genome sequence of this E. coli strain has been determined recently. Phylogenetic analysis suggests that it is very closely related to a group of E. coli strains known as Shigella boydii, Shigella flexerni and Shigella sonnei. However, the ‘free-living’ strain appears to lack the virulence factors found in the Shigella strains. Shigella are significant human diarrheal pathogens and are unlikely to persist in a vertebrate host for a significant period. Consequently, Shigella strains are likely to possess attributes that enhance their persistence in non-host environments. The genome sequences of these Shigella strains are also available and this provides the opportunity to investigate what traits might contribute to the enhanced survival of these bacteria in the external environment.

This project will take a comparative genomics and phenomics approach to investigate the similarities and differences between the free-living E. coli strains and the Shigella strains. The study not only has the potential to identify what traits enhance the survival of these bacteria, but may also lead to a better understanding of the traits present in the Shigella that may contribute to the virulence of these strains.

The research will provide the student with experience in a variety of basic microbiological techniques and familiarity with a variety of comparative genomics techniques. No previous experience with micro-organisms is required. This project is suitable for a February or July start.