Inactivation of Cellobiose Dehydrogenases Modifies the Cellulose Degradation Mechanism of Podospora anserina.
Conversion of biomass into high-value products, including biofuels, is of great interest to developing sustainable biorefineries. Fungi are an inexhaustible source of enzymes to degrade plant biomass. Cellobiose dehydrogenases (CDHs) play an important role in the breakdown through synergistic action with fungal lytic polysaccharide monooxygenases (LPMOs). The three CDH genes of the model fungus Podospora anserina were inactivated, resulting in single and multiple CDH mutants. We detected almost no difference in growth and fertility of the mutants on various lignocellulose sources, except on crystalline cellulose, on which a 2-fold decrease in fertility of the mutants lacking P. anserina CDH1 (PaCDH1) and PaCDH2 was observed. A striking difference between wild-type and mutant secretomes was observed. The secretome of the mutant lacking all CDHs contained five beta-glucosidases, whereas the wild type had only one. P. anserina seems to compensate for the lack of CDH with secretion of beta-glucosidases. The addition of P. anserina LPMO to either the wild-type or mutant secretome resulted in improvement of cellulose degradation in both cases, suggesting that other redox partners present in the mutant secretome provided electrons to LPMOs. Overall, the data showed that oxidative degradation of cellulosic biomass relies on different types of mechanisms in fungi.



Plant biomass degradation by fungi is a complex process involving dozens of enzymes. The roles of each enzyme or enzyme class are not fully understood, and utilization of a model amenable to genetic analysis should increase the comprehension of how fungi cope with highly recalcitrant biomass. Here, we report that the cellobiose dehydrogenases of the model fungus Podospora anserina enable it to consume crystalline cellulose yet seem to play a minor role on actual substrates, such as wood shavings or miscanthus. Analysis of secreted proteins suggests that Podospora anserina compensates for the lack of cellobiose dehydrogenase by increasing beta-glucosidase expression and using an alternate electron donor for LPMO.
University of Paris Diderot, Sorbonne Paris Cité, Laboratoire Interdisciplinaire des Energies de Demain, Paris, France.
Narumon
N
Tangthirasunun
INRA, Aix Marseille Université, Polytech Marseille, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France.
David
D
Navarro
INRA, Aix Marseille Université, Polytech Marseille, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France.
Sona
S
Garajova
INRA, UMR1319 Micalis, Plateforme d'Analyse Protéomique de Paris Sud-Ouest, Jouy-en-Josas, France.
Didier
D
Chevret
University of Paris Diderot, Sorbonne Paris Cité, Laboratoire Interdisciplinaire des Energies de Demain, Paris, France.
Laetitia Chan Ho
LCH
Tong
University of Paris Diderot, Sorbonne Paris Cité, Laboratoire Interdisciplinaire des Energies de Demain, Paris, France.
Valérie
V
Gautier
Center of Excellence in Fungal Research and School of Science, Mae Fah Luang University, Chiang Rai, Thailand.
Kevin D
KD
Hyde
University of Paris Diderot, Sorbonne Paris Cité, Laboratoire Interdisciplinaire des Energies de Demain, Paris, France philippe.silar@univ-paris-diderot.fr jean-guy.berrin@univ-amu.fr.
Philippe
P
Silar
INRA, Aix Marseille Université, Polytech Marseille, UMR1163 Biodiversité et Biotechnologie Fongiques, Marseille, France philippe.silar@univ-paris-diderot.fr jean-guy.berrin@univ-amu.fr.|INRA, UMR1319 Micalis, Plateforme d'Analyse Protéomique de Paris Sud-Ouest, Jouy-en-Josas, France.
Jean-Guy
JG
Berrin
D002237:Carbohydrate Dehydrogenases / Q000235:genetics* / Q000378:metabolism; D002482:Cellulose / Q000378:metabolism*; D004789:Enzyme Activation / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D010641:Phenotype; D010802:Phylogeny; D048468:Podospora / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism
D005656:Fungal Proteins; D002482:Cellulose; D002237:Carbohydrate Dehydrogenases; C019859:cellobiose-quinone oxidoreductase
Podospora anserina; biomass degradation; cellobiose dehydrogenase