CRISPR/Cas9: A cutting-edge tool for cellulase enhancement in fungi

CRISPR/Cas9 system is a cutting-edge gene-editing tool that has recently been introduced for the strain improvement of fungi to enhance their cellulolytic activity. Cellulase is an enzyme complex that hydrolyzes cellulosic fraction of lignocellulosic biomass into glucose which can be converted subsequently into biofuels and other value-added products. Among diverse microbial communities, fungi are considered the most potent cellulolytic candidates but the naturally low cellulase titers have been the major bottleneck in using them for industrial and biotechnological applications. However, CRISPR/Cas9 mediated fungal strain engineering has opened up new avenues to overcome this challenge by enabling precise and efficient genome editing which induces the overexpression of cellulase genes, deletion of cellulase repressors, and alterations in the regulatory elements governing the overall cellulase gene expression. The effective CRISPR/Cas9 systems have already been designed for the functional genome editing of industrially competent cellulolytic fungal strains such as Aspergillus strains, Trichoderma reesei, and Penicillium chrysogenum, however, the technological advancements to establish it across the fungal kingdom are still desired. The employment of CRISPR/Cas9 in fungal strain improvement poses various limitations such as off-target effects, the need for designing suitable delivery methods, and the appropriate selection markers, therefore, future research should focus on addressing these issues and further refining the CRISPR/Cas9 system for fungal strain improvement. Conclusively, this RNA-directed DNA endonuclease system is a promising future tool for improving cellulase production in fungi leading to the development of numerous industrially competent strains, thus, supporting the sustainable development goal (SDG 7) of affordable and clean energy through efficient bioconversion of lignocellulosic biomass into biofuels coupled with other value-added products.