Regulation of the Enzymes of the meta-Cleavage Pathway of Pseudomonas putida: The Regulon is Composed of Two Operons

Abstract

In P. putida NCIB10015 the gene determining phenol hydroxylase is in a separate operon from the genes determining catechol 2,3-oxygenase and subsequent enzymes of the meta-cleavage pathway. In the wild-type strain, non-coordinate induction of phenol hydroxylase and catechol 2,3-oxygenase occurred when catechol, phenol or isomers of cresol were used as inducers. Phenol hydroxylase was repressed to a greater extent than catechol 2,3-oxygenase when induced by phenol in the presence of either benzoate or acetate. In a mutant deficient in catechol 2,3-oxygenase, 3- or 4-methylcatechol repressed formation of phenol hydroxylase but not of enzymes functioning later in the pathway. Four mutants had an altered regulatory element that resulted in different effects on the expression of phenol hydroxylase and catechol 2,3-oxygenase genes when isomers of cresol were used as inducers. Repression of enzyme induction by acetate, benzoate or 3- or 4-methylcatechol showed that catechol 2,3-oxygenase and subsequent meta-cleavage pathway genes form part of the same operon. Benzoate or 3- or 4-methylcatechol repressed phenol hydroxylase but none of the other enzymes in the pathway, while acetate coordinately repressed catechol 2,3-oxygenase and subsequent enzymes.