Characterisation of a novel thermostable endoglucanase from Alicyclobacillus vulcanalis of potential application in bioethanol production.

A novel endoglucanase encoding gene was cloned from Alicyclobacillus vulcanalis and expressed in E. coli. The deduced amino acid sequence showed highest identity with α-L-arabinofuranosidase-like proteins from glycoside hydrolase family 51. The recombinant enzyme was purified by affinity chromatography and characterised in terms of its potential suitability for lignocellulose hydrolysis at high temperature in the production of bioethanol. The purified enzyme displayed maximum activity at 80 °C and pH 3.6-4.5. Tween 20 was found to have a beneficial effect on enzyme activity and thermal stability. When incubated in the presence of 0.1% Tween 20, the enzyme retained full activity after 72 h at 70 °C and 78% of original activity after 72 h at 75 °C. Maximum activity was observed on carboxymethyl cellulose, and the purified enzyme also hydrolysed lichenan, barley β-glucan and xylan. The purified enzyme decreased the viscosity of carboxymethyl cellulose when assessed at 70-85 °C and was capable of releasing reducing sugars from acid-pretreated straw at 70 and 75 °C. The results indicate the potential suitability of the enzyme for industrial application in the production of cellulosic bioethanol.