Potent Fungal Chitinase for the Bioconversion of Mycelial Waste

Aspergillus niger mycelial waste is a good raw material for production of N-acetyl-D-glucosamine (GlcNAc). In this study, AnChiB, an A. niger chitinase which is upregulated during autolysis, was found to degrade A. niger mycelial waste with high efficiency. It could produce 1.45 mM (GlcNAc) 2 in 8 h from raw mycelial waste, outperforming other chitinases, including bacterial SmChiA, human HsCht, and insect Of ChtI and Of Chi-h. The crystal structure of AnChiB was determined, and residues Trp(106) and Trp(118) were found to be important for the activity of AnChiB toward mycelial waste; mutation of either Trp(106) or Trp(118) into phenylalanine or alanine resulted in dramatically decreased activity. A recombinant strain of Bacillus subtilis was constructed to extracellularly produce AnChiB, and the culture supernatant was used to treat mycelial waste. This eco-friendly strategy could produce 3.7 mM of GlcNAc from 10 g of mycelial waste in 94 h with a yield of 71.3%.