Figure 1.
Comparative Genome Browser. In a subgroup of the γ-Proteobacteria, two ancient operons for adjacent steps in the TCA cycle, sdhCDAB and sucABCD, have been merged into one larger operon. This view from the Comparative Genome Browser shows the sdhA locus across an archaeon (Halobacterium sp.), a Gram-positive bacterium (Mycobacterium tuberculosis), and a diverse range of proteobacteria. Note that the larger operon is present in only a single clade, yet it is highly conserved within this group, suggesting that it may reflect a recent innovation within the γ-Proteobacteria.
