**3. Conclusions**

Cellulolytic enzymes are found in various living systems, but the main destroyers of cellulose are microorganisms, primarily microscopic aerobic fungi, as well as various types of aerobic and anaerobic bacteria. Fungi from the genus *Trichoderma* are the most widely used industrial producers of cellulases in different countries, from which intensive research on cellulases began.

Using the methods of mutagenesis, selection, and genetic engineering, highly productive *T. reesei* strains capable of secreting up to 100 g/l of extracellular protein were obtained. Some species of fungi from the genus *Penicillium* (in particular *P. verruculosum*) have great prospects as an alternative to *T. reesei*, producing cellulase complexes whose enzymes have significantly higher specific activity compared to *T. reesei* cellulases. Highly productive mutant strains of *P.verruculosum* capable of secreting up to 60 g/l of extracellular protein were obtained. Based on the *P. verruculosum* strain, a host-vector system has been created that allows the expression of homologous and heterologous genes and the production of enzyme preparations, the qualitative and quantitative composition of which is appropriately optimized in terms of ensuring its maximum activity in relation to various types of cellulose-containing plant raw materials.
