Expression and characterisation of a thermophilic endo-1,4-beta-glucanase from Sulfolobus shibatae of potential industrial application

An endo-1,4-beta-d-glucanase gene was cloned from the thermophilic archaea Sulfolobus shibatae and expressed in E. coli. The recombinant enzyme was purified by heat denaturation and affinity chromatography prior to characterisation. The purified recombinant enzyme exhibited maximum activity at 95-100 A degrees C and displayed a broad pH profile with over 91% of its maximum activity observed at pH 3-5. Upon assessment of enzyme thermal stability, full activity was observed after 1 h incubation at 75, 80 and 85 A degrees C while 98%, 90% and 84% of original activity was detected after 2 h at 75, 80 and 85 A degrees C, respectively. Maximum activity was observed on barley beta-glucan and lichenan and the purified enzyme also hydrolysed CMC and xylan. Endoglucanase activity was confirmed by viscometric assay with a rapid decrease in substrate viscosity observed immediately upon incubation with barley beta-glucan or CMC. The crude enzyme released reducing sugars from acid-pretreated straw at 75-85 A degrees C. The thermophilic nature and biochemical properties of the enzyme indicate its potential suitability in industrial applications undertaken at high temperature, such as the production of second-generation bioethanol from lignocellulosic feedstocks and in the brewing industry. This is the first known report of an endoglucanase from S. shibatae.