ИСТИНА

Enzyme cost is one of the crucial factors in economically feasible production of second generation biofuels, such as ethanol or butanol derived from plant lignocellulosic biomass. The major components of the lignocellulosic feedstock are cellulose and hemicelluloses. Cellulases and hemicellulases, catalyzing the biodegradation of these polysaccharides into soluble fermentable sugars, are typically produced by industrial strains of filamentous fungi. In order to realize the biotechnology of the biomass conversion to liquid fuels and other useful products on large-scale, different tasks should be solved. One of the most important tasks is finding more active cellulases and their producers. Since 1970s mutant strains of Trichoderma reesei have been considered indisputable champions in cellulase production and enzyme activity among the biomass-degrading fungi. So, it is not surprising that most of R&D projects on bioethanol production from lignocellulosics have been based on T. reesei cellulases. However, recent data from different laboratories have increasingly demonstrated that alternatives to T. reesei enzymes in saccharification of lignocellulosic feedstocks exist. In particular, some fungal species belonging to the genera Penicillium as well as mutant strains of Myceliophthora thermophila may represent such alternatives. The strategy of creating the highly-effective cellulase fungal producers included the following steps: • Finding out the key enzymes responsible for the biodegradation of different lignocellulosic residues; • Rational design of multienzyme compositions for efficient lignocellulosic hydrolysis; testing various enzyme mixes on different pretreated biomass samples; • Increasing the secretion of the key enzymes; cloning and homologous or heterologous expression of the missing enzymes and/or deletion of useless genes; • Production of the optimal multienzyme compositions using recombinant mutant fungal strains with high protein production ability. When equalized either by cellulase activity or by protein concentration in the reaction system, novel enzyme preparations produced by Penicillium and M. thermophila mutant strains usually displayed higher saccharification performance in hydrolysis of different lignocellulosic residues than commercial cellulase preparations produced by modern mutant strains of T. reesei or, at least, were comparable to them by saccharification performance. Some of the novel mutant fungal strains provided protein production on a level with the highest standards for protein production by fungi.