Cloning and Heterologous Expression of the Phenazine Biosynthetic Locus from Pseudomonas aureofaciens 30-84. Leland S. Pierson III. Agricultural Research Service, U.S. Department of Agriculture, Root Disease and Biological Control Research Unit, Washington State University, Pullman 99164-6430 U.S.A. Linda S. Thomashow. Agricultural Research Service, U.S. Department of Agriculture, Root Disease and Biological Control Research Unit, Washington State University, Pullman 99164-6430 U.S.A. MPMI 5:330-339. Accepted 13 April 1992. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1992.

Pseudomonas aureofaciens strain 30-84 suppresses take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. Three antibiotics, phenazine-1-carboxylic acid, 2-hydroxyphenazine-1-carboxylic acid, and 2-hydroxyphenazine, were responsible for disease suppression. Tn5-induced mutants deficient in production of one or more of the antibiotics (Phz‾) were significantly less suppressive than the parental strain. Cosmids pLSP259 and pLSP282 from a genomic library of strain 30-84 restored phenazine production and fungal inhibition to 10 different Phz‾ mutants. Sequences required for production of the phenazines were localized to a segment of approximately 2.8 kilobases that was present in both cosmids. Expression of this locus in Escherichia coli required the introduction of a functional promoter, was orientation-specific, and resulted in the production of all three phenazine antibiotics. These results strongly suggest that the cloned sequences encode a major portion of the phenazine biosynthetic pathway.