Purification and biochemical characterization of a novel mesophilic glucoamylase from Aspergillus tritici WZ99.

Glucoamylase, cleaving the nonreducing end of starch releasing glucose, is an important enzyme in starch processing. The optimal temperature for industrial glucoamylase activity is 60-70°C, which is not compatible with the optimal growth temperature for Saccharomyces cerevisiae. In this study, 26 fungal strains producing amylolytic activities that were more active at 30°C than at 60°C were isolated from 151 environmental samples. Fungal strain WZ99, producing extracellular amylolytic activities with the lowest optimal temperature at 40°C, was identified as Aspergillus tritici by analysis of morphological and molecular data. An extracellular glucoamylase was purified from A. tritici WZ99. The optimal pH of the enzyme was 4.0-5.0 and optimal temperature was 45°C. The glucoamylase was stable at pH 4.5-10.0 and below 40°C. Metal ions at four concentrations did not inhibit the enzyme activity. The glucoamylase contained a catalytic domain belonging to glycosyl hydrolase family 15 and thus was named as AtriGA15A. The enzyme shared the highest identity of 54% with a glucoamylase from Rasamsonia emersonii. This glucoamylase showing excellent comprehensive enzymatic characteristics might have potential applications in starch-based bioethanol production and starch processing.