Figure 4. Maximum likelihood phylogenetic tree of the 20 Escherichia coli and Shigella strains as reconstructed from the sequences of the 1878 genes of the Escherichia core genome.

The earliest diverging species, E. fergusonii, was chosen to root the tree. The numbers at the nodes correspond, in black, to the bootstrap values (1000 bootstraps) and, in grey, to a “consensus strength”, which is the number of genes that confirms the bipartition (see Materials and Methods). The latter value is displayed only in instances where consensus and tested trees correspond. The branch length separating E. fergusonii from the E. coli strains is not to scale; the numbers above the branch indicate its length. Phylogenetic group membership of the strains is indicated with bars at the right of the figure.