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  • 1
    Electronic Resource
    Electronic Resource
    Evolution of aromatic biosynthesis and fine-tuned phylogenetic positioning of Azomonas, Azotobacter and rRNA group I pseudomonads (1986)
    Springer
    Archives of microbiology 144 (1986), S. 222-227 
    Details
    ISSN: 1432-072X
    Keywords: Phylogeny ; Biochemical evolution ; Aromatic biosynthesis ; Azomonas ; Azotobacter ; Pseudomonas ; Regulatory enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The evolutionary history of biochemical pathways can be determined in microbial groupings for which phylogenetic trees have been established. This has been demonstrated best in Superfamily B, an assemblage of rRNA homology groups containing lineages that lead to genera such as Escherichia and other enteric microbes, Pseudomonas (Group I), Xanthomonas, Oceanospirillum, and Acinetobacter. The rRNA homology group that defines Group I pseudomonads also includes Azomonas and Azotobacter, but particular dendrogram points of evolutionary divergence for these genera within Superfamily B have not been established. Phylogenetic relationships at such intergeneric levels can be deduced by analysis of aromaticpathway enzyme arrangement and regulation in selected groupings where dynamic evolutionary changes have occurred. A case in point is illustrated by Axomonas insignis, Azotobacter paspali, and Azotobacter vinelandii — a grouping that appears to be homogeneous with respect to the evolutionary state of the aromatic pathway. The conclusion that this phylogenetic cluster diverges from an ancestor common to pseudomonad subgroup Ia (rather than to subgroup Ib) is based upon the absence of chorismate mutase-F and arogenate dehydratase, enzymes making up a twostep pathway of phenylalanine biosynthesis that is absent in subgroup Ia, but present in subgroup Ib. Of further interest, Azomonas insignis and Azotobacter sp. were found to comprise a distinctive and recently evolved sublineage, differing from subgroup Ia species in their loss of a regulatory isozyme of 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (ADHP synthase-trp) that is subject to feedback inhibition by l-tryptophan. DAHP synthase-trp is an ancient character state of Superfamily B that has been retained during the evolutionary history of most members of this Superfamily.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00410951
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  • 2
    Electronic Resource
    Electronic Resource
    Evolution of L-phenylalanine biosynthesis in rRNA homology group I of Pseudomonas (1983)
    Springer
    Archives of microbiology 136 (1983), S. 163-168 
    Details
    ISSN: 1432-072X
    Keywords: Phylogeny ; Biochemical evolution ; Aromatic pathway ; L-Phenylalanine ; Pseudomonads
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Group I pseudomonads exhibit diversity for L-phenylalanine biosynthesis that is a basis for separation of two subgroups. Subgroup Ib (fluorescent species such as Pseudomonas aeruginosa, P. fluorescens, or P. putida) possesses an unregulated overflow pathway to Lphenylalanine, together with a second, regulated pathway. Subgroup Ia (non-fluorescent species such as P. stutzeri, P. mendocia, or P. alcaligenes) possess only the regulated pathway to L-phenylalanine. Thus, subgroup Ia species lack an unregulated isozyme of chorismate mutase and arogenate dehydratase, enzymes which are thought to divert chorismate to L-phenylalanine under conditions of high carbon input into aromatic biosynthesis. A priori the overflow pathway could have been either lost in subgroup Ia or gained in subgroup Ib. Since Group V pseudomonads (mainly Xanthomonas) are known to branch off from the Group I lineage at a deeper phylogenetic level than the point of divergence for subgroups Ia and Ib, the presence of the overflow pathway in Group V pseudomonads reveals that the overflow pathway must have been lost in the evolution of subgroup Ia. All Group I species possess a bifunctional protein (P-protein) which catalyzes both chorismate mutase and prephenate dehydratase reactions. In subgroup Ia species this highly conserved protein must be the sole source of prephenate to be used for tyrosine biosynthesis. Thus, the channeling action of the P-protein whereby chorismate is committed towards L-phenylalanine formation can be negated by selective feedback inhibition exerted by L-phenylalanine upon the prephenate dehydratase component of the P-protein. Diversion of prephenate molecules under the latter conditions towards L-tyrosine comprises a channel-shuttle mechanism. Such an essential role of the P-protein chorismate mutase for both tyrosine and phenylalanine formation is supported by the observation that stringent phenylalanine auxotrophs lacked the prephenate dehydratase activity but not chorismate mutase activity of the P-protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409838
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  • 3
    Electronic Resource
    Electronic Resource
    Evolutionary implications of features of aromatic amino acid biosynthesis in the genus Acinetobacter (1985)
    Springer
    Archives of microbiology 143 (1985), S. 122-129 
    Details
    ISSN: 1432-072X
    Keywords: Phylogeny ; Biochemical evolution ; Aromatic biosynthesis ; Acinetobacter ; Regulatory enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Key enzymes of aromatic amino acid biosynthesis were examined in the genus Acinetobacter. Members of this genus belong to a suprafamilial assemblage of Gram-negative bacteria (denoted Superfamily B) for which a phylogenetic tree based upon oligonucleotide cataloging of 16S rRNA exists. Since the Acinetobacter lineage diverged at an early evolutionary time from other lineages within Superfamily B, an examination of aromatic biosynthesis in members of this genus has supplied improtant clues for the deduction of major evolutionary events leading to the contemporary aromatic pathways that now exist within Superfamily B. Together with Escherichia coli, Pseudomonas aeruginosa and Xanthomonas campestris, four well-spaced lineages have now been studied in comprehensive detail with respect to comparative enzymological features of aromatic amino acid biosynthesis. A. calcoaceticus and A. lwoffii both possess two chorismate mutase isozymes: one a monofunctional isozyme (chorismate mutase-F), and the other (chorismate mutase-P) a component of a bifunctional P-protein (chorismate mutase-prephenate dehydratase). While both P-protein activities were feedback inhibited by l-phenylalanine, the chorismate mutase-P activity was additionally inhibited by prephenate. Likewise, chorismate mutase-F was product inhibited by prephenate. Two isozymes of 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase were detected. The major isozyme (〉95%) was sensitive to feedback inhibition by l-tyrosine, whereas the minor isozyme was apparently insensitive to allosteric control. Prephenate dehydrogenase and arogenate dehydrogenase activities were both detected, but could not be chromatographically resolved. Available evidence favors the existence of a single dehydrogenase enzyme, exhibiting substrate ambiguity for prephenate andl-arogenate. Dehydrogenase activity with either of the latter substrates was specific for NADP+, NAD+ being ineffective. Consideration of the phylogeny of Superfamily-B organisms suggests that the stem ancestor of the Superfamily possessed a single dehydrogenase enzyme having ambiguity for both substrate and pyridine nucleotide cofactor. Since all other members of Superfamily B have NAD+-specific dehydrogenases, specialization for NADP+ must have occurred following the point of Acinetobacter divergence, leading to the dichotomy seen in present-day Superfamily-B organisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00411034
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