The recent evolutionary origin of the phenylalanine-sensitive isozyme of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase in the enteric lineage of bacteria

Abstract

Evolutionary events that generated the three regulatory isozymes of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase present in contemporary strains of Escherichia coli have been proposed recently [Ahmad et al. (1986) J Bacteriol 165:146-154]. The phylogenetic subdivision of gram-negative prokaryotes studied (Superfamily B) includes enteric bacteria, an Oceanospirillum cluster, pseudomonad Group I (e.g., Pseudomonas aeruginosa), pseudomonad Group V (e.g., Xanthomonas), and the Acinetobacter grouping. DAHP synthase-phe, a regulatory isozyme subject to allosteric control by L-phenylalanine, was the last member of the isozyme family to evolve. Thus, DAHP synthase-phe is absent throughout Superfamily B except within the enteric lineage. Bacteria that make up the enteric lineage (Escherichia, Klebsiella, Erwinia, Serratia, Proteus, Aeromonas, and Alteromonas) were examined in detail; DAHP synthase-phe was present in each of these organisms. Therefore, the isozyme originated between the separation of the enteric and Oceanospirillum lineages, prior to the divergence of Alteromonas putrefaciens (44% homology with E. coli by DNA:rRNA hybridization) from the rest of the enteric lineage. DAHP synthase-tyr and DAHP synthase-trp were uniformly present within the enteric lineage, although it was often necessary to derepress DAHP synthase-trp by physiological manipulation in order to demonstrate its presence.