ABSTRACT
Nutritional criteria serve as the basis for taxonomic schemes with high predictive value, and sequence studies suggest that genes do not drift in response to the vicissitudes of life in microbial populations. The presence of different metabolic mechanisms for dissimilation of protocatechuate suggests that variants of the pathway evolved independently from separate genetic backgrounds in fungi and bacteria. Transcriptional controls that underlie the induction patterns of bacteria presumably are highly evolved traits, and highly evolved traits tend to be conserved. The duplicated enol-lactone hydrolase genes diverged widely as they co-evolved in Acinetobacter, and it is instructive to consider selective forces that favor the extensive divergence of homologous genes as they co-evolve within a single cell line. It is likely that selective forces favoring divergence away from homologous sequences are less discriminating than forces favoring acquisition of a specific binding site or catalytic site in a protein.
