PHENAZINE ANTIBIOTIC BIOSYNTHESIS IN PSEUDOMONAS-AUREOFACIENS-30-84 IS REGULATED BY PHZR IN RESPONSE TO CELL-DENSITY

We have identified a gene that acts in trans to activate the expressio n of the phenazine biosynthetic genes in the biological control organi sm Pseudomonas aureofaciens 30-84. This gene, phzR (phenazine regulato r), is located upstream of and divergently transcribed from the phenaz ine biosynthetic genes, Thus, the phenazine biosynthetic locus consist s of at least two divergently transcribed operons. A functional phzR g ene is required for phenazine production. The nucleotide sequence of p hzR revealed an open reading frame of 723 nucleotides encoding a prote in of ca. 27 kDa. The predicted amino acid sequence of PhzR has homolo gy with other bacterial positive transcriptional activators, including LasR of Pseudomonas aeruginosa, LuxR of Vibrio fischerii, and TraR of Agrobacterium tumefaciens. The addition of cell-free supernatants fro m late-exponential-phase cultures of strain 30-84 resulted in expressi on of a genomic phzB::lacZ reporter strain at a lower cell density tha n normal, indicating the possible presence of an autoinducer. These re sults indicate that PhzR is a member of a two-component sensor-regulat or family with known or predicted carboxy-terminal DNA-binding domains which regulates gene expression in response to environmental and cell density signals.