Glucoamylase (exo-1,4- -d-glucan glucanohydrolase, EC 3.2.1.3) is the major starch-degrading enzyme secreted by the phytopathogenic fungus Colletotrichum gloeosporioides

Abstract

Activity assays based on selective product detection were used to identify the classes of amylase present in culture filtrates of the phytopathogen Colletotrichum gloeosporioides. When transferred from a glucose medium to a medium containing starch as sole carbohydrate, C. gloeosporioides secreted amylolytic activity into liquid shake cultures starting 2-3 d after inoculation, and produced levels of activity up to 0.45 IU ml−1 (assayed by the p-hydroxybenzoic acid hydrazide — PAHBAH — reducing sugar method), about 20 times higher than the activity in comparable glucose-grown controls, suggesting that starch (or a starch degradation product) was required to induce amylase synthesis. In four separate experiments, the ratio of total reducing sugar production (assayed by the PAHBAH method) to glucose production (assayed by the glucose-specific glucose oxidase — GO — method) was about 1.0 in most samples of culture filtrate, clearly demonstrating that the major amylolytic enzyme secreted by C. gloeosporioides is a glucoamylase (exo-1,4-a-d-glucan glucanohydrolase, EC 3.2.1.3, synonym amylogluco-sidase). On one occasion only (a 7 d sample in one experiment) was evidence obtained for a-amylase (endo-1,4-a-d-glucan glucanohydrolase, EC 3.2.1.1) also being present in the culture filtrate (PAHBAH/GO ratio 1.37); the presence of a-amylase in this sample was confirmed by native polyacrylamide gel electrophoresis using a starch-iodine activity stain.