CARBON CATABOLITE REPRESSION OF PHENOL DEGRADATION IN PSEUDOMONAS-PUTIDA IS MEDIATED BY THE INHIBITION OF THE ACTIVATOR PROTEIN PHLR

Enzymes involved in (methyl)phenol degradation of Pseudomonas putida I t are encoded by the catabolic operon (phlA-L) on plasmid pPGH1. Trans cription of this operon by the sigma(54) (RpoN)-containing RNA polymer ase is positively controlled by the gene product of the divergently tr anscribed phlR in response to the availability of the respective subst rate. Additionally, phenol degradation is subject to carbon catabolite repression induced by organic acids (e.g., succinate, lactate, and ac etate) or carbohydrates (e.g., glucose and gluconate). Analysis of lac Z fusion to the catabolic promoter and quantified primer extension exp eriments indicate that carbon catabolite repression also occurs at the transcriptional level of the catabolic operon. In this study, it is f urthermore shown that carbon catabolite repression is a negative contr ol. Titration of the postulated negative controlling factor was exclus ively observed when extra copies of functional phlR gene were present in the cell. We therefore conclude that PhlR is the target and that ca rbon catabolite repression of phenol degradation occurs by interfering with the activating function of PhlR.