Isolation of a Clostridiumthermocellum gene encoding a thermostable β-1, 3-glucanase (laminarinase)

A Clostridiumthermocellum gene directing the synthesis of a thermostable β-glucanase was localized on a 1.9-kb DNA fragment by subcloning into Escherichiacoli plasmid vectors. The enzyme was highly efficient in degrading glucans with alternating β-1, 3- and β-1,4-linkages such as lichenan and barley glucan. It was also active towards the β-1, 3-glucan laminarin, but lacked activity on cellulosic substrates and α-glucans. The enzyme was therefore classified as β-1, 3-glucanase (laminarinase) and the corresponding gene was designated licA. With barley β-glucan as substrate the enzyme had a pH optimum around pH 6.5 and a temperature optimum at 65°C. It was stable for several hours at 60°C in the absence of substrate.