Mycelial glucoamylases produced by the thermophilic fungus Scytalidium thermophilum strains 15.1 and 15.8: purification and biochemical characterization

Two strains (15.1 and 15.8) of the thermophilic fungus Scytalidium thermophilum produced high levels of intracellular glucoamylases, with potential for industrial applications. The isoform I of the glucoamylase produced by 15.1 strain was sequentially submitted to DEAE-Cellulose and CM-Cellulose chromatography, and purified 141-fold, with 5.45% recovery. The glucoamylase of strain 15.8 was purified 71-fold by CM- Cellulose and Concanavalin A-Sepharose chromatography, with 7.38% recovery. Temperature and pH optima were in the range of 50-60°C and 5.0-6.0, respectively, using starch and maltose as substrates. The glucoamylase of S. thermophilum 15.8 was more stable (t50 > 60 min) than that of S. thermophilum 15.1 (t50= 11-15 min), at 60°C. The glucoamylase activities were enhanced by several ions (e.g. Mn(2+) and Ca(2+)) and inhibited by β- mercaptoethanol. The glucoamylase from 15.1 strain showed a Km of 0.094 mg/ml and 0.029 mg/ml and Vmax of 202 U/mg prot and 109 U/mg prot, for starch and maltose, respectively. The hydrolysis products of starch and maltose, analyzed by TLC, demonstrated glucose as end product and confirming the character of the enzyme as glucoamylase. Differences were observed in relation to the products formed with maltose as substrate between the two strains studied. S. thermophilum 15.8 formed maltotriose in contrast with S. thermophilum 15.1.