Phylogeny of the γ-Proteobacteria. The phylogeny was derived from concatenated alignments of highly conserved proteins (see Materials and methods). In this study, we focused on evolutionary events after the divergence of Shewanella spp. from Escherichia coli K12 (the shaded portion of the tree). The β-Proteobacteria formed a sister group to the γ-Proteobacteria. The scale bar corresponds to 5% amino acid divergence.