The evolutionary pattern of aromatic amino acid biosynthesis and the emerging phylogeny of pseudomonad bacteria

Abstract

Pseudomonad bacteria are a phylogenetically diverse assemblage of species named within contemporary genera that include Pseudomonas, Xanthomonas and Alcaligenes. Thus far, five distinct rRNA homology groups (Groups I through V) have been established by oligonucleotide cataloging and by rRNA/DNA hybridization. A pattern of enzymic features of aromatic amino acid biosynthesis (enzymological patterning) is conserved at the level of rRNA homology, five distinct and unambiguous patterns therefore existing in correspondence with the rRNA homology groups. We sorted 87 pseudomonad strains into Groups (and Subgroups) by aromatic pathway patterning. The reliability of this methodology was tested in a blind study using coded cultures of diverse pseudomonad organisms provided by American type Culture Collection. Fourteen of 14 correct assignments were made at the Group level (the level of rRNA homology), and 12 of 14 correct assignments were made at the finer-tuned Subgroup levels. Many strains of unknown rRNA-homology affiliation had been placed into tentative rRNA groupings based upon enzymological patterning. Positive confirmation of such strains as members of the predicted rRNA homology groups was demonstrated by DNA/rRNA hybridization in nearly every case. It seems clear that the combination of these molecular approaches will make it feasible to deduce the evolution of biochemical-pathway construction and regulation in parallel with the emerging phylogenies of microbes housing these pathways.

Deoxyribonucleic Acid Similarities among Pseudomonas Species

“…Strains of different Pseiidomonas species within each of the rRNA groups share substantial degrees of rRNA similarity (3,27), while most of the DNA sequences seem to have undergone considerable divergence, as judged by the low levels of DNA similarity obtained in hybridization experiments (25; this paper). In contrast, strains of different species of other genera may show in their DNAs a degree of conservatism approaching that of the ribosomal genes (18).…”

“…Recently, a recommendation has been made for the rejection of the epithet panici, which was not meant to be applied to fluorescent organisms (11); however, the strain included in our studies, as well as in the studies of other workers (3,7,28,30), is definitely a pathovar of P. syringae, although its origin is unclear.…”

“…Thus, three strains of the species were examined by Stanier et al ( 3 9 , who found them to be typical fluorescent pseudomonads and to correspond to P.flfluorescens biotype G. On the other hand, one strain studied by Lysenko (20) produced no fluorescent pigment but had yellowish colonies and produced a diffusible brown pigment. Recently, this strain was examined by Byng et al (3) for its rRNA composition and was assigned to rRNA group V. In all of the papers by this group of workers this organism is included under the name P . geniculata.…”

“…The organisms used in this study were the same as those used in a previous rRNA similarity study (3). All were obtained from the American Type Culture Collection, Rockville, Md.…”

Evolution of 3-deoxy- d - arabino -heptulosonate-7-phosphate synthase-encoding genes in the yeast Saccharomyces cerevisiae

“…Mammals convert Phe to Tyr and use aromatic amino acids as precursors for numerous important substances including neurotransmitters like serotonin (7). In Escherichia coli, the three isogenes aroF (8), aroG (9) and aroH (10) code for three DAHPS isoenzymes, each feedback-regulated by one of the aromatic amino acids Tyr (AroF), Phe (AroG), and Trp (AroH), respectively (11). Total cellular DAHPS activities are unequally distributed to the three isoenzymes.…”