Deletion of AA9 Lytic Polysaccharide Monooxygenases Impacts A. nidulans Secretome and Growth on Lignocellulose

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Fanchini Terrasan, Cesar Rafael ; Rubio, Marcelo Ventura ; Gerhardt, Jaqueline Aline ; Franco Cairo, Joao Paulo ; Contesini, Fabiano Jares ; Zubieta, Mariane Paludetti ; de Figueiredo, Fernanda Lopes ; Valadares, Fernanda Lima ; Ribeiro Correa, Thamy Livia ; Murakami, Mario Tyago ; Franco, Telma Teixeira ; Davies, Gideon J. ; Walton, Paul H. ; Damasio, Andre

• Document type: Journal article
• Source: MICROBIOLOGY SPECTRUM; v. N/A, p. 16-pg., 2022-06-06.

Abstract

Lytic polysaccharide monooxygenases (LPMOs) are oxidative enzymes found in viruses, archaea, and bacteria as well as eukaryotes, such as fungi, algae and insects, actively contributing to the degradation of different polysaccharides. In Aspergillus nidulans, LPMOs from family AA9 (AnLPMO9s), along with an AA3 cellobiose dehydrogenase (AnCDH1), are cosecreted upon growth on crystalline cellulose and lignocellulosic substrates, indicating their role in the degradation of plant cell wall components. Functional analysis revealed that three target LPMO9s (AnLPMO9C, AnLPMO9F and AnLPMO9G) correspond to cellulose-active enzymes with distinct regioselectivity and activity on cellulose with different proportions of crystalline and amorphous regions. AnLPMO9s deletion and overexpression studies corroborate functional data. The abundantly secreted AnLPMO9F is a major component of the extracellular cellulolytic system, while AnLPMO9G was less abundant and constantly secreted, and acts preferentially on crystalline regions of cellulose, uniquely displaying activity on highly crystalline algae cellulose. Single or double deletion of AnLPMO9s resulted in about 25% reduction in fungal growth on sugarcane straw but not on Avicel, demonstrating the contribution of LPMO9s for the saprophytic fungal lifestyle relies on the degradation of complex lignocellulosic substrates. Although the deletion of AnCDH1 slightly reduced the cellulolytic activity, it did not affect fungal growth indicating the existence of alternative electron donors to LPMOs. Additionally, double or triple knockouts of these enzymes had no accumulative deleterious effect on the cellulolytic activity nor on fungal growth, regardless of the deleted gene. Overexpression of AnLPMO9s in a cellulose-induced secretome background confirmed the importance and applicability of AnLPMO9G to improve lignocellulose saccharification. IMPORTANCE Fungal lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that boost plant biomass degradation in combination with glycoside hydrolases. Secretion of LPMO9s arsenal by Aspergillus nidulans is influenced by the substrate and time of induction. These findings along with the biochemical characterization of novel fungal LPMO9s have implications on our understanding of their concerted action, allowing rational engineering of fungal strains for biotechnological applications such as plant biomass degradation. Additionally, the role of oxidative players in fungal growth on plant biomass was evaluated by deletion and overexpression experiments using a model fungal system. Fungal lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that boost plant biomass degradation in combination with glycoside hydrolases. Secretion of LPMO9s arsenal by Aspergillus nidulans is influenced by the substrate and time of induction. (AU)

• FAPESP's process: 15/50612-8 - An integrated approach to explore a novel paradigm for biofuel production from lignocellulosic feedstocks
• Grantee: Telma Teixeira Franco
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 15/50590-4 - Lignin valorization in cellulosic ethanol plants: biocatalytic conversion via ferulic acid to high value chemicals
• Grantee: Fábio Márcio Squina
• Support Opportunities: Program for Research on Bioenergy (BIOEN) - Thematic Grants
• FAPESP's process: 17/22669-0 - N-glycosylation and enzymes secretion in filamentous fungi
• Grantee: André Ricardo de Lima Damasio
• Support Opportunities: Program for Research on Bioenergy (BIOEN) - Regular Program Grants
• FAPESP's process: 16/16306-0 - Functional and biological analyses of LPMO (Lytic Polysaccharide Monooxigenases) and accessory proteins (non-CAZymes) for degradation of sugarcane straw by filamentous fungi
• Grantee: César Rafael Fanchini Terrasan
• Support Opportunities: Scholarships in Brazil - Post-Doctoral