Localization of Glucose Oxidase with Immunocytochemistry in the Biocontrol Fungus Talaromyces flavus

ABSTRACT Production of the enzyme glucose oxidase has been shown to be involved in the biological control of Verticillium wilt by Talaromyces flavus. In this study, the location of glucose oxidase was determined in T. flavus by immunocytochemistry using glucose oxidase-specific polyclonal antibody. Immunostaining revealed that glucose oxidase was both intracellular and extracellular. Old, as well as young, hyphal cells contained glucose oxidase, but labeling of the cell wall-associated enzyme decreased as the cells aged. Exocytosis rather than cell lysis was the primary means of release of glucose oxidase from cells. Enzyme stability studies confirmed that the glucose oxidase of T. flavus is an extremely stable enzyme, retaining 13% of its original activity after 2 weeks at 25 degrees C and retaining activity for several days at temperatures up to 50 degrees C.