Production of novel pullulanases at high concentrations by two newly isolated thermophilic clostridia

Abstract

Two thermophilic bacteria, which are capable of growing on starch at 60–70°C under anaerobic conditions, were isolated from a sugar refinery in Uelzen and from Solar lake in Israel. On the basis of their physiological characteristics they were identified as Clostridium thermohydrosulfuricum Uel 1 and C. thermohydrosulfuricum Sol 1, respectively. The product pattern of glucose polymer hydrolysis showed that both strains secreted enzymes' that possess amylolytic and pullulytic activities. The major product formed was maltose. In addition, α-glucosidase activity could be detected in the supernatants of Uel 1 strain. Compared to most anaerobes investigated these isolates secreted extremely high concentrations of pullulanases in batch culture. Up to 85% of the total enzyme synthesized was detected in the culture fluid. Unlike the pullulanases of tyoe I, which can only attack the α-1,6-glycosidic linkages, the pullulanases of both clostridial strains were also capable of hydrolyzing α-1,4-linkages. The enzyme system of both bacteria was found to be highly thermoactive; optimal activity was detected at pH 5.0 and 85°C. Even at 95°C and without the addition of metal ions still 15% to 25% of enzymatic activity was detectable.