Induction of extracellular arabinases on monomeric substrates in Aspergillus niger

Abstract

The induction of extracellular arabinases by pentose sugars and polyols generated by the metabolic pathway of l-arabinose and d-xylose catabolism in Aspergillus niger was investigated. Induction occurred with l-arabinose and l-arabitol but not with d-xylose or xylitol. l-arabitol in particular was found to be a good inducer for α-l-arabinofuranosidase and endo-arabinase activities. Western blotting analysis showed both α-l-arabinofuranosidase A and B to be present. No induction was observed using d-arabitol. Unlike the wild type A. niger N402 strain, the A. niger xylulose kinase negative mutant N572 also showed induction of α-l-arabinofuranosidases A and B and endo-arabinase activity on d-xylose and xylitol. This is due to metabolic conversion of these compounds leading to the accumulation of both xylitol and l-arabitol in this mutant, the latter of which then acts as inducer. The induction of the two α-l-arabinofuranosidases and endo-arabinase is under the control of two regulatory systems namely pathway specific induction and carbon catabolite repression. Under derepressing conditions in the wild type only α-l-arabinofuranosidase B could be detected by Western blotting analysis. This indicates that α-l-arabinofuranosidase B is of importance in the initiation of specific induction of the various arabinose activities in A. niger grown on arabinose containing structural polysaccharides.