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Physiology and Biochemistry

Identification of a Metabolite Produced by Talaromyces flavus as Glucose Oxidase and its Role in the Biocontrol of Verticillium dahliae. K. K. Kim, Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, Beltsville, MD 20705; D. R. Fravel, and G. C. Papavizas. Soilborne Diseases Laboratory, Plant Protection Institute, U.S. Department of Agriculture, Beltsville, MD 20705. Phytopathology 78:488-492. Accepted for publication 21 October 1987. 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, 1988. DOI: 10.1094/Phyto-78-488.

A metabolite produced in liquid culture by Talaromyces flavus that mediated inhibition of radial growth and germination of microsclerotia of Verticillium dahliae was identified as glucose oxidase ( β -d-glucose:oxygen oxidoreductase, EC 1.1.3.4). A semipurified preparation of glucose oxidase per se from the culture filtrate or of a commercial preparation of glucose oxidase per se was not active against microsclerotia. However, both exhibited antibiotic activity against microsclerotia when glucose was added to the preparation. Thus, antibiotic activity present in crude culture filtrates may be due to the action of hydrogen peroxide released by the reaction catalyzed by glucose oxidase. The minimum in vitro concentration of hydrogen peroxide necessary to inhibit germination of microsclerotia was approximately 12 μg ml^–1. The molecular weight of the glucose oxidase in filtrates was estimated to be 173,000. The enzyme displayed a very high specificity for d-glucose as a substrate with apparent K_m of 100 mM of α and β anomeric mixture of glucose when the activity was monitored by a bioassay against microsclerotia of V. dahliae. The optimum activity of the enzyme occurred in a solid agar matrix of pH 5.0.