title: Investigating Aspergillus nidulans secretome during colonisation of cork cell walls.
abstract: Cork, the outer bark of Quercus suber, shows a unique compositional structure, a set of remarkable properties, including high recalcitrance. Cork colonisation by Ascomycota remains largely overlooked. Herein, Aspergillus nidulans secretome on cork was analysed (2DE). Proteomic data were further complemented by microscopic (SEM) and spectroscopic (ATR-FTIR) evaluation of the colonised substrate and by targeted analysis of lignin degradation compounds (UPLC-HRMS). Data showed that the fungus formed an intricate network of hyphae around the cork cell walls, which enabled polysaccharides and lignin superficial degradation, but probably not of suberin. The degradation of polysaccharides was suggested by the identification of few polysaccharide degrading enzymes (β-glucosidases and endo-1,5-α-l-arabinosidase). Lignin degradation, which likely evolved throughout a Fenton-like mechanism relying on the activity of alcohol oxidases, was supported by the identification of small aromatic compounds (e.g. cinnamic acid and veratrylaldehyde) and of several putative high molecular weight lignin degradation products. In addition, cork recalcitrance was corroborated by the identification of several protein species which are associated with autolysis. Finally, stringent comparative proteomics revealed that A. nidulans colonisation of cork and wood share a common set of enzymatic mechanisms. However the higher polysaccharide accessibility in cork might explain the increase of β-glucosidase in cork secretome.
  
  
  CONCLUSIONS
  Cork degradation by fungi remains largely overlook. Herein we aimed at understanding how A. nidulans colonise cork cell walls and how this relates to wood colonisation. To address this, the protein species consistently present in the secretome were analysed, as well as major alterations occurring in the substrate, including lignin degradation compounds being released. The obtained data demonstrate that this fungus has superficially attacked the cork cell walls apparently by using both enzymatic and Fenton-like reactions. Only a few polysaccharide degrading enzymes could be detected in the secretome which was dominated by protein species associated with autolysis. Lignin degradation was corroborated by the identification of some degradation products, but the suberin barrier in the cell wall remained virtually intact. Comparative proteomics revealed that cork and wood colonisation share a common set of enzymatic mechanisms.
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal; Instituto de Biologia Experimental e Tecnológica (IBET), Apartado 12, 2781-901 Oeiras, Portugal.
authors: Isabel
authors: I
authors: Martins
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors: Helga
authors: H
authors: Garcia
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal; Instituto Nacional de Investigação Agrária e Veterinária, (INIAV), Av. da República, Quinta do Marquês, 2784-505 Oeiras, Portugal.
authors: Adélia
authors: A
authors: Varela
authors: Department of Analytical Chemistry, University of Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
authors: Oscar
authors: O
authors: Núñez
authors: Proteomics Platform, Centre de Recherche Public -Gabriel Lippmann, Belvaux, Luxembourg.
authors: Sébastien
authors: S
authors: Planchon
authors: Department of Analytical Chemistry, University of Barcelona, Diagonal 645, E-08028 Barcelona, Spain.
authors: Maria Teresa
authors: MT
authors: Galceran
authors: Proteomics Platform, Centre de Recherche Public -Gabriel Lippmann, Belvaux, Luxembourg.
authors: Jenny
authors: J
authors: Renaut
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal.
authors: Luís P N
authors: LP
authors: Rebelo
authors: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, 2780-157 Oeiras, Portugal; Instituto de Biologia Experimental e Tecnológica (IBET), Apartado 12, 2781-901 Oeiras, Portugal. Electronic address: spereira@itqb.unl.pt.
authors: Cristina
authors: C
authors: Silva Pereira
mesh_terms: D001233:Aspergillus nidulans / Q000378:metabolism*; D002473:Cell Wall / Q000382:microbiology*; D005656:Fungal Proteins / Q000378:metabolism*; D024301:Plant Bark / Q000166:cytology / Q000382:microbiology*; D020543:Proteome / Q000378:metabolism*; D029963:Quercus / Q000166:cytology / Q000382:microbiology*; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D005656:Fungal Proteins; D020543:Proteome; D001617:beta-Glucosidase
keywords: Alcohol oxidase; Aspergillus nidulans; Cork; Fenton-like reactions; Lignin degradation; Secretome