Very big difference
Two groups (Perna et al and Hayashi et al) went further. Whatever differences exist between the two strains must in part determine what makes O157 a killer, something we would very much like to understand. They therefore sequenced the genomes of different E. coli O157:H7 strains, computationally predicted the proteins encoded by the genomes, and compared these sets of protein to that of the laboratory strain E. coli K12.

While the two strains turned out to share almost all of the core genes that make E. coli what it is, the pathogen O157 has an astonishing 22% more genes than the laboratory strain. To put this in perspective, the relatively more distant cousins humans and chimps differ almost not at all in their sets of genes

How could this enormous difference arise? How does it relate to the pathogenicity of E. coli O157?

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