Physiological and molecular aspects of degradation of plant polysaccharides by fungi: What have we learned from Aspergillus?

Abstract

Plant biomass is the most abundant and usable carbon source for many fungal species. Due to its diverse and complex structure, fungi need to produce a large range of enzymes to degrade these polysaccharides into monomeric components. The fine-tuned production of such diverse enzyme sets requires control through a set of transcriptional regulators. Aspergillus has a strong potential for degrading biomass, thus this genus has become the most widely studied group of filamentous fungi in this area. This review examines Aspergillus as a successful degrader of plant polysaccharides, and reviews its potential in many industries such as biofuel and as a production host of homologous and heterologous proteins.

Genomics Review of Holocellulose Deconstruction by Aspergilli

“…Genome-wide reports comparing Aspergillus flavus with A. oryzae (27) and A. nidulans with A. fumigatus and A. oryzae (28) and a curated comparative genomics resource for aspergilli (29) are available as well. Several articles describing plant cell wall-degrading enzymes have been published, mainly focusing on glycoside hydrolases (30, 31) or fungal sets of plant polysaccharide-degrading enzymes (32,33), as well as comparisons of A. nidulans with A. niger and A. oryzae (34)(35)(36). The last comprehensive review of cellulose-and hemicellulose-degrading enzymes produced by Aspergillus was published in 2001 (37).…”

Overexpression, purification and characterisation of homologous α-l-arabinofuranosidase and endo-1,4-β-d-glucanase in Aspergillus vadensis

“…Not only does Aspergillus growth excel under fermentation conditions with an exceptional capacity of secreting high levels of homologous product but also their potential in plant polysaccharide degradation and the extensive set of enzyme mixes which they secrete for this purpose is also well recognised [9]. To date, much of this research has been focused on A. niger and A. oryzae, while the capacity of A. vadensis, a close relative of A. niger, has remained largely unexplored.…”

“…Comparative analysis to A. niger AbfA three enzymes: β-1,4-d-glucosidase, cellobiohydrolase and β-1,4-d-endoglucanase. In contrast, the hydrolysis of xylan requires the combined action of at least nine different enzymes: α-l-arabinofuranosidase, α-1,4-d-galactosidase, α-glucuronidase, acetylxylan esterase, arabinoxylan arabinofuranohydrolase, β-1,4-d-xylosidase, feruloyl esterase, β-1,4-d-galactosidase and β-1,4-d-endoxylanase [9]. The ability to produce such a broad range of enzymes combined with their good fermentation capabilities has resulted in many studies being dedicated to the development of Aspergillus as hosts for the industrial production of recombinant proteins [15].…”

“…This in turn, opens up sites for subsequent attack by cellobiohydrolases, which cleave cellulose chains at the ends and release cellobiose. These oligosaccharides are then further degraded into d-glucose molecules by the action of β-glucosidases and exoglucanases [9,33]. Among the most efficient producers of cellulolytic enzymes, in particular endo-1,4-β-d-glucanase, is the filamentous fungus A. niger which has gained it significant interest especially in the food, textile and pharmaceutical industries [13].…”

Transcriptional Regulation and Responses in Filamentous Fungi Exposed to Lignocellulose

“…This chapter will focus on the ascomycetes. There are already several extensive reviews related to the regulatory responses of fungi to small molecules as well as, but less so, to lignocellulose [9,[11][12][13][14][15][16][17][18]. We will therefore refer to the reviewed information where applicable and expand the discussion to focus on exposure of fungi to lignocellulose.…”