title: Chitinases CtcB and CfcI modify the cell wall in sporulating aerial mycelium of Aspergillus niger.
abstract: Sporulation is an essential part of the life cycle of the industrially important filamentous fungus Aspergillus niger. The formation of conidiophores, spore-bearing structures, requires remodelling of the fungal cell wall, as demonstrated by the differences in carbohydrate composition of cell walls of vegetative mycelium and spores. Glycoside hydrolases that are involved in this process have so far remained unidentified. Using transcriptome analysis, we have identified genes encoding putative cell-wall-modifying proteins with enhanced expression in sporulating aerial mycelium compared to vegetative mycelium. Among the most strongly induced genes were those encoding a protein consisting of a putative chitin binding module (CBM14) and the chitinolytic enzymes NagA, CfcI and CtcB. Reporter studies showed that the N-acetyl-β-hexosaminidase gene nagA was expressed both in vegetative hyphae and in aerial structures (aerial hyphae, conidiophores and conidia) upon starvation. In contrast, promoter activities of the chitinase genes ctcB and cfcI were specifically localized in the conidiophores and conidia. CtcB is an endo-chitinase and CfcI releases monomers from chitin oligosaccharides: together these enzymes have the potential to degrade chitin of the fungal cell wall. Inactivation of both the cfcI and ctcB genes affected neither radial growth rate, nor formation and germination of spores. The amount of chitin in the spore walls of a ΔcfcIΔctcB double deletion strain, however, was significantly increased compared with the wild-type, thus indicating that CfcI and CtcB indeed modify the A. niger cell walls during sporulation. These novel insights in the sporulation process in aspergilli are of strong scientific relevance, and also may aid industrial strain engineering.
authors.affiliation: Microbial Physiology Research Group, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands.
authors.forename: Jolanda M
authors.initials: JM
authors.lastname: van Munster
authors.affiliation: Institute of Biology Leiden, Molecular Microbiology and Biotechnology, Kluyver Centre for Genomics of Industrial Fermentation, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Nitsche
authors.affiliation: Microbiology and Kluyver Centre for Genomics of Industrial Fermentation, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Pauline
authors.initials: P
authors.lastname: Krijgsheld
authors.affiliation: Aquatic Biotechnology and Bioproduct Engineering Department, Institute for Technology and Management (ITM), University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
authors.forename: Alle
authors.initials: A
authors.lastname: van Wijk
authors.affiliation: Microbial Physiology Research Group, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands.
authors.forename: Lubbert
authors.initials: L
authors.lastname: Dijkhuizen
authors.affiliation: Microbiology and Kluyver Centre for Genomics of Industrial Fermentation, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
authors.forename: Han A
authors.initials: HA
authors.lastname: Wösten
authors.affiliation: Institute of Biology Leiden, Molecular Microbiology and Biotechnology, Kluyver Centre for Genomics of Industrial Fermentation, Leiden University, Sylviusweg 72, 2333 BE Leiden, The Netherlands.
authors.forename: Arthur F
authors.initials: AF
authors.lastname: Ram
authors.affiliation: Aquatic Biotechnology and Bioproduct Engineering Department, Institute for Technology and Management (ITM), University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.|Microbial Physiology Research Group, Groningen Biomolecular Sciences and Biotechnology Institute (GBB), University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands.
authors.forename: Marc J E C
authors.initials: MJEC
authors.lastname: van der Maarel
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism*; D002688:Chitinases / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D025282:Mycelium / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D013172:Spores, Fungal / Q000201:enzymology / Q000235:genetics / Q000254:growth & development
chemical_list: D005656:Fungal Proteins; D002688:Chitinases