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Researchers sequence strain of E. coli linked to disease
Bacterial genome is compared to that of a harmless laboratory strain
  
By
Edward R. Winstead


To identify genes that turn benign bacteria into agents of disease, researchers have sequenced the genome of Escherichia coli 0157:H7 and compared the sequence to that of its harmless cousin, a non-virulent laboratory strain. The comparison revealed 1,387 new genes found only in the killer bacterium, providing a list of gene candidates for virulent traits in an organism that can cause death in a matter of days following infection. The sequenced pathogen was isolated from ground beef linked to contaminated hamburgers that caused deaths in an E. coli outbreak in 1982.

E. coli is commonly found in the human gastrointestinal system, and it comes in both beneficial and harmful forms. Nicol T. Perna, of the University of Wisconsin, Madison, and colleagues used the 'whole-genome shotgun' approach to sequence the bacterium's roughly 4.1 million units of DNA. The researchers report in Nature that the virulent and the laboratory strains have 'an unexpectedly complex segmented relationship.' The genomes share a common sequence (the 'backbone') that is punctuated by hundreds of sections of DNA that are unique to one strain or the other. These 'islands' contain 1,387 genes unique to the 0157:H7 strain and 528 genes unique to the laboratory strain, K-12 MG1655.

In a News and Views piece entitled "Gastrogenomics," Jonathan A. Eisen, of the Institute for Genomic Research, in Rockville, Maryland, notes that DNA islands on 0157:H7 include many known genes associated with disease. Some of these genes may encode factors needed to make the adhesive filaments that help the bacterium stick to the lining of the gut, for example, but their roles in the development of disease are unproved, he writes.

Though many questions remain, the process of answering those questions has begun. "One of the great things about genomics is that the data it provides allow nearly any group, any where in the world, to start seeking answers to outstanding questions immediately," writes Eisen.

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Perna, N.T. et al. Genome sequence of enterohaemorrhagic Escherichia coli O157:H7. Nature 409, 529-533 (January 25, 2001).
 
Eisen, J.A. Gastrogenomics. Nature 409, 463-466 (January 25, 2001).
 

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