Metabolic Plasmid Organization and Distribution
Pseudomonas strains carry plasmids under regulation of natural and synthetic organic residues and bear primary roles in mineralization. Aromatic compounds of known oxidation pathways provide convenient models for genetic analyses and for plasmid DNA isolation and structure determination. The alkane and terpene catabolic systems, coded on larger self-fertile plasmids, have provided primary data on gene organization and regulation, as well as plasmid chromosome gene redundancy.
Two aromatic plasmids, HAH7 and SAL1, of about 80 to 90 kb (kilobases), code respectively the conversion of naphthalene and of salicylate to the anaplerotic intermediates, pyruvate and acetaldehyde, plus CO, or formate, thus supporting cell growth. The NAH plasmid codes for these two conversions on separate operons, both controlled by salicylate or anthrinilate. Operon 1 codes the conversion of naphthalene to salicylate; operon 2, salicylate via catechol with “meta“ (2,3 oxygenase) aromatic ring cleavage. Plasmid DNA isolated from wild type and transposon Tn5 induced insertion mutants was scored for defective loci by enzyme assays in the genomes subjected to gel electrophoresis after restriction digestion. An EcoRl digest fragment A of 23 kilobases carries the bulk of both operons; Smal yields 5 fragments, A of 42 kilobases and B of 18. The latter which lacks the left hand 5+ kilobases of EcoRl A reveals that the replicon in the nahA gene are within this 5 kilobase region. The transcription is from left to right in both operons; an 8 to 10 kilobase segment between the operons carries at least one regulatory locus. The cell plasmid in Smal digest yields 5 fragments identical in size to those of NAH7, plus two smaller, about 3 kb, segments which constitute an insertion in naphthalene operon 1 in the gene AB region. The methuds now available for plasmid isolation and DNA analyses, the genetic scoring and cloning, now appear capable of providing, in the near future, a complete structure, organization, and regulation model of the aromatic plasmids in fluorescent Pseudontonas species.
KeywordsFluorescent Pseudomonad Ring Fission Catechol Dioxygenase Naphthalene Oxidation Catabolic Plasmid
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