FIG. 9.

Tracking milestone evolutionary events in the group Bacteroidetes/Chlorobi. The dendrogram (not drawn to scale) enumerates character states inferred to be present in the common ancestor of the superphylum at the top. Various evolutionary events affecting genes of the ancestral trp and aro operons are indicated at appropriate lineage positions. At the bottom, the gene organizations of the trp operons and the aro operons present in contemporary classes of the phylum Bacteroidetes are shown.