Authors: A F A Chimphango S H Rose W H van Zyl J F Görgens
Publish Date: 2012/03/30
Volume: 95, Issue: 1, Pages: 101-112
Abstract
A recombinant strain of the proteasedeficient nonacidifying pH mutant Aspergillus niger D15 A niger D15 abfB strain was developed to secrete αlarabinofuranosidase AbfB free of endo14βxylanases for selective hydrolysis of xylan into hydrogels The A niger D15 abfB strain expressed the αlarabinofuranosidase abfB gene under the transcriptional control of the glyceraldehyde3phosphate dehydrogenase promoter gpd P and glucoamylase terminator glaA T in fermentation cultures containing 10 glucose The yield activity purity kinetics and ability of the recombinant AbfB to selectively hydrolyse xylans into hydrogels were assessed The recombinant AbfB secreted in 125mL shake flasks and 10L bioreactor fermentation cultures had specific activities against ρnitrophenylαarabinofuranoside of up to 44 and 27 U g−1 dry weight respectively In addition the recombinant AbfB was present as a single protein species on silverstained 10 sodium dodecyl sulphatepolyacrylamide gel electrophoresis The recombinant AbfB had optimal activity at 40–55 °C and pH 30 to pH 50 and was stable at temperature and pH of up to 60 °C and pH 60 respectively About 20 of the available arabinose in the xylan was released by the recombinant AbfB from the hydrolysis of low viscosity wheat and oat spelt arabinoxylans and about 9 and 5 from bagasse and bamboo arabinoglucuronoxylans respectively that led to the formation of the hydrogels Therefore the constructed A niger D15 abfB strain presented a microbial system for the production of recombinant AbfB with the required purity for the modification of xylans into hydrogelsThe authors acknowledge the technical services and material support received from Dr JF Alberts Ms A Hugo Mr M Mathews Prof B Prior Dr T de Villiers and Ms J Cilliers of Microbiology Department Stellenbosch University Mr E James Ms H Botha Prof J Snoep and Mr A Arendse of Biochemistry Department Stellenbosch University Dr P van Zyl of the Center for Scientific and Industrial Research Prof AMF Milagres of the School of Engineering University of Sáo Paulo Brazil This study was funded by The National Research Fund Department of Science and Technology Andrew Mellon Fellowship and Center for Renewable and Sustainable Energy Studies South African National Energy Research Institute
Keywords: