Growth medium composition-determined regulatory mechanisms are superimposed on CatR-mediated transcription from the pheBA and catBCA promoters in Pseudomonas putida

Department of Genetics, Institute of Molecular and Cell Biology, Estonian Biocentre and Tartu University, Riia 23, 51010 Tartu, Estonia 1 Author for correspondence: Maia Kivisaar. Tel: +372 7 375015. Fax: +372 7 420286. e-mail: maiak{at}ebc.ee Expression of the phenol degradation pathway in Pseudomonas putida strain PaW85 requires coordinated transcription of the plasmid-borne pheBA operon encoding catechol 1,2-dioxygenase and phenol monooxygenase, respectively, and the chromosomally encoded catechol degradation catBCA operon. Transcriptional activation from the pheBA and catBCA promoters is regulated by CatR and the catechol degradation pathway intermediate cis , cis -muconate. Here it is shown that physiological control mechanisms are superimposed on this regulatory system. Transcriptional activation from the pheBA and catBCA promoters is growth-phase-regulated in P. putida cells grown on rich medium (LB medium). CatR-mediated transcription from these promoters is silenced on rich medium until the transition from exponential to stationary phase. A slight positive effect (threefold) of stationary-phase-specific sigma factor S on transcription from the pheBA promoter was observed. Expression of the catBCA promoter was not influenced by the activity of this sigma factor. In contrast to rich growth medium, transcription from the pheBA and catBCA promoters in minimal medium containing a mixture of glucose and sodium benzoate was rapidly induced in exponential culture. It was shown that the presence of amino acids in the culture medium causes exponential silencing of the pheBA and catBCA promoters. The possibility that a hypothetical repressor protein could be involved in physiological control of transcription from the pheBA and catBCA promoters is discussed. Keywords: pheBA , catBCA , operons, exponential silencing of transcription Abbreviations: CCM, cis , cis -muconate; ß-Gal, ß-galactosidase