Structural genes for salicylate biosynthesis from chorismate in Pseudomonas aeruginosa

Mol Gen Genet. 1995 Nov 15;249(2):217-28. doi: 10.1007/BF00290369.


Salicylate is a precursor of pyochelin in Pseudomonas aeruginosa and both compounds display siderophore activity. To elucidate the salicylate biosynthetic pathway, we have cloned and sequenced a chromosomal region of P. aeruginosa PAO1 containing two adjacent genes, designated pchB and pchA, which are necessary for salicylate formation. The pchA gene encodes a protein of 52 kDa with extensive similarity to the chorismate-utilizing enzymes isochorismate synthase, anthranilate synthase (component I) and p-aminobenzoate synthase (component I), whereas the 11 kDa protein encoded by pchB does not show significant similarity with other proteins. The pchB stop codon overlaps the presumed pchA start codon. Expression of the pchA gene in P. aeruginosa appears to depend on the transcription and translation of the upstream pchB gene. The pchBA genes are the first salicylate biosynthetic genes to be reported. Salicylate formation was demonstrated in an Escherichia coli entC mutant lacking isochorismate synthase when this strain expressed both the pchBA genes, but not when it expressed pchB alone. By contrast, an entB mutant of E. coli blocked in the conversion of isochorismate to 2,3-dihydro-2,3-dihydroxybenzoate formed salicylate when transformed with a pchB expression construct. Salicylate formation could also be demonstrated in vitro when chorismate was incubated with a crude extract of P. aeruginosa containing overproduced PchA and PchB proteins; salicylate and pyruvate were formed in equimolar amounts. Furthermore, salicylate-forming activity could be detected in extracts from a P. aeruginosa pyoverdin-negative mutant when grown under iron limitation, but not with iron excess. Our results are consistent with a pathway leading from chorismate to isochorismate and then to salicylate plus pyruvate, catalyzed consecutively by the iron-repressible PchA and PchB proteins in P. aeruginosa.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Chorismic Acid / metabolism*
  • Cloning, Molecular
  • Genes, Bacterial*
  • Intramolecular Transferases*
  • Kinetics
  • Molecular Sequence Data
  • Mutagenesis
  • Mutagenesis, Insertional
  • Pseudomonas aeruginosa / genetics*
  • Pseudomonas aeruginosa / metabolism*
  • Pyruvates / metabolism
  • Recombinant Proteins / metabolism
  • Restriction Mapping
  • Salicylates / metabolism*
  • Sequence Homology, Amino Acid


  • Bacterial Proteins
  • Pyruvates
  • Recombinant Proteins
  • Salicylates
  • pchB protein, Pseudomonas aeruginosa
  • Intramolecular Transferases
  • PchA protein, Pseudomonas aeruginosa
  • Chorismic Acid

Associated data

  • GENBANK/X82644