Abstract: A method is described for the enzymatic saccharification of a cellulosic substrate to glucose which utilizes fermentation of the substrate with the cellulase enzyme complex-producing, thermophilic microorganism Microbispora bispora Rutgers P&W and its mutants. The resistance of M. bispora Rutgers P&W cellulase to end-product inhibition enables conversion efficiency superior to that of known cellulase producing microorganisms. Continued enzyme activity at elevated temperatures allows broader applicability of enzyme-catalyzed saccharification than heretofore attained. The microorganism in its purified form incubated on cellulase, and its cellulolytic mutants, are also disclosed.