A GLOBAL REGULATOR OF SECONDARY METABOLITE PRODUCTION IN PSEUDOMONAS-FLUORESCENS PF-5

Mutations in the apdA (for antibiotic production) gene of the plant ro ot-colonizing bacterium Pseudomonas fluorescens Pf-5 pleiotropically a bolish the production of an array of antibiotics, including pyrrolnitr in, pyoluteorin, and 2,4-diacetylphloroglucinol, as well as the produc tion of tryptophan side chain oxidase, hydrogen cyanide, and an extrac ellular protease. The lack of production of secondary metabolites by A pdA(-) mutants was correlated with the loss of inhibition of the phyto pathogenic fungus Rhizoctonia solani in culture. Sequencing of the apd A region identified an open reading frame of 2,751 bp. The predicted a mino acid sequence of the apdA gene contains conserved domains of the histidine kinases that serve as sensor components of prokaryotic two-c omponent regulatory systems. The apdA nucleotide and predicted amino a cid sequences are strikingly similar to the sequences of lemA and repA , genes encoding putative sensor kinases that are required for the pat hogenicity of Pseudomonas syringae pv. syringae and Pseudomonas viridi flava, respectively. Introduction of the cloned apdA(+) gene restored the wild-type phenotype to both LemA(-) mutants of P. syringae and Apd A(-) mutants of Pf-5. The 101-kDa ApdA protein reacted with an anti-Le mA antiserum, further demonstrating the similarity of ApdA to LemA. Th ese results show that apd4 encodes a putative sensor kinase component of a classical two-component regulatory system that is required for se condary-metabolite production by P. fluorescens Pf-5.