A Cellulolytic and Xylanolytic Enzyme Complex from an Alkalothermoanaerobacterium, Tepidimicrobium xylanilyticum BT14

Abstract

A cellulolytic and xylanolytic enzyme complex-producing alkalothermoanaerobacterium strain, Tepidimicrobium xylanilyticum BT14 is described. The cell was Gram-positive, rod-shaped and endospore-forming. Based on 16S rRNA gene analysis and various lines of biochemical and physiological properties, the strain BT14 was a new member of the genus Tepidimicrobium. The strain BT14 cells had ability to bind to Avicel, xylan and corn hull. The pH and temperature optima for growth were 9.0 and 60 degrees C, respectively. The strain BT14 was able to use a variety of carbon sources. When the bacterium was grown on corn hulls under an anaerobic condition, a cellulolytic and xylanolytic enzyme complex was produced. Crude enzyme containing cellulase and xylanase of the strain BT14 was active in broad ranges of pH and temperature. The optimum conditions for cellulase and xylanase activities were pH 8.0 and 9.0 at 60 degrees C, respectively. The crude enzyme had ability to bind to Avicel and xylan. The analysis of native-PAGE and native-zymograms indicated the cellulose-binding protein showing both cellulase and xylanase activities while SDS-PAGE zymograms showed 4 bands of cellulases and 5 bands of xylanases. Evidence of cohesin-like amino acid sequence seemed to indicate that the protein complex shared direct relationship to the cellulosome of Clostridium thermocellum. The crude enzyme from the strain BT14 showed effective degradation of plant biomass. When grown on corn hulls at pH 9.0 and 60 degrees C under anaerobic conditions, the strain BT14 produced ethanol and acetate as the main fermentation products.