Efficient biomass degradation into fermentable sugars is still a major challenge
in the biotechnology field. The heterogeneity and structural complexity of the fiber make
enzyme action difficult. Fungi belonging to the phylum Ascomycota and Basidiomycota, as
pathogenic or saprophytic organisms, are adapted to infect/obtain nutrients from various
carbon and nitrogen sources, including several kinds of wood, soil, and organic waste
materials. According to genomic, proteomic and biochemical data, the efficiency of fungi
to break down plant cell walls is due to their capacity to produce a wide range of
CAZymes. These microorganisms have a complex machinery to secrete a broad spectrum
of enzymes for releasing carbon and nitrogen locked in complex substrates for nutrition.
The majority of proteins secreted by filamentous fungi are glycosylated and their capacity
to secrete proteins is probably faster than their synthesis. In spite of their efficiency, the
production level of many proteins of interest in natural strains is too low for commercial
exploitation. However, industrial strains have shown remarkable improvements in protein
secretion yield after traditional mutagenesis techniques. The first part of this chapter is
focused on polysaccharide structures and covers the main fungal enzymes used as a
strategy for its degradation. Then, a revision on the heterologous expression of
hemicellulases by filamentous fungi hosts will be presented, along with the main
bottlenecks in fungal heterologous expression. Finally, we provide an extensive revision of
the commercial enzymes derived from filamentous fungi systems.
Keywords: Aspergillus nidulans, Aspergillus niger, auxiliary enzymes, client
proteins, cellulases, filamentous fungi, hemicellulases, heterologous expression,
plant biomass, plant cell wall, Trichoderma reesei.
