Fig. 8.

Schematic representation of the phylum Proteobacteria. Black lines indicate the sequence of appearance of Proteobacteria classes as described by Gupta et al. [56]: δ and ε-Proteobacteria (eight orders, light blue), α-Proteobacteria (ten orders, light pink), β-Proteobacteria (eight orders, light green) and γ-Proteobacteria (nineteen orders, light yellow). Within each class, orders that contain species that carry cluster 2-like sequences are written in color (color-code as in Fig. 9). Asterisks indicate orders where we identified gene clusters that resemble cluster 2 with some alteration in gene order/composition (see text)