REGULATION OF TRANSCRIPTION OF THE PHENOL DEGRADATION pheBA OPERON IN PSEUDOMONAS PUTIDA

During growth of Pseudomonas in nutritionally rich environment many catabolicoperons are repressed by physiological control mechanisms. In the current reportwe have studied mechanisms that down-regulate transcription from the CatR-controlled promoter of phenol degradation genes pheBA in P. putida whenbacteria are growing in the presence of amino acids. We found that the amount ofcis,cis-muconate (CCM) which is an effector molecule for the CatR regulator andan intermediate of the catechol degradation pathway in P. putida, limits transcrip-tion from the pheBA promoter. Comparison of expression profiles from thepheBA promoter in P. putida wild type strain PaW85 and in its catB mutantderivative unable to degrade CCM demonstrated that cellular concentration ofCCM is a limiting factor determining the level of transcription from the pheBApromoter. Although the amount of CCM is probably always below the levelsthat would allow maximal rate of transcription from the pheBA promoter, the limitation became most significant in rich medium-grown cells. Results of thecurrent study provide a new experimental evidence that composition of thegrowth media influences transcription from the pheBA promoter by modulating the expression of the pheB-encoded catechol 1,2-dioxygenase which degrades catechol to CCM at the level of synthesis of this enzyme. To our knowledge,this is a first time to show that physiological control of catabolic operons in