Identification of a Metabolite Produced byTalaromyces flavusas Glucose Oxidase and its Role in the Biocontrol ofVerticillium dahliae

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Abstract
A metabolite produced in liquid culture by Talaromyces flavus that meditated inhibition of radial growth and germination of microsclerotia of Verticillium dahliae was identified as glucose oxidase (.BETA.-D-glucose:oxygen oxidoreductase, EC 1.1.3.4). A semipurified preparation of glucose oxidase per se from the culture fitrate or of a commercial preparation of glucose oxidase per se was not active against microsclerotia. However, both exhibited antibitotic activity against microslerotia 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 necessary to inhibit germination of microsclerotia was approximately 12 .mu.g ml-1. The molecular weight of the glucose oxidase in fitrates was estimated to be 173,000. The enzyme displayed a very high specificity for D-glucose as a substrate with apparent Km of 100 mM of .alpha. and .beta. 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 matix of pH 5.0.

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