Characterization of an antibiotic produced by a strain of Pseudomonas fluorescens inhibitory to Gaeumannomyces graminis var. tritici and Pythium spp.

The production, isolation, and characterization of an antibiotic substance from cultures of Pseudomonas fluorescens 2-79 (NRRL B-15132) is described. P. fluorescens 2-79 originally was isolated from the roots of wheat and is suppressive to the wheat root disease take-all caused by Gaeumannomyces graminis var. tritici. The antibiotic was isolated from potato glucose broth cultures of strain 2-79 by solvent extraction. It was purified by silica gel column chromatography and was a greenish yellow, needle-shaped crystal with a melting point of 242 degrees C (decomposition). It was soluble in methylene chloride, chloroform, acetone, 2 N sodium hydroxide, and 2 N hydrochloric acid and was insoluble in water, methanol, ethyl acetate, tetrahydrofuran, diethyl ether, carbon tetrachloride, hexane, and petroleum ether. On the basis of UV, infrared, 1H-nuclear magnetic resonance, 13C-nuclear magnetic resonance, mass spectral analysis, and elemental analysis, the structure of the antibiotic is proposed to be a dimer of phenazine carboxylic acid. Lithium aluminum hydride reduction of the antibiotic yielded hydroxymethyl phenazine as a major product which retained most of the biological characteristics of the parent molecule. There were no toxic symptoms when mice received this antibiotic by oral doses up to 464 mg/kg. The antibiotic showed excellent activity against several species of fungi, including the wheat pathogens Gaeumannomyces graminis var. tritici, Rhizoctonia solani, and Pythium aristosporum; and it may have a role in suppression of take-all in vivo by strain 2-79.