Induction and Optimization of Chitosanase Production by Aspergillus fumigatus YT-1 Using Response Surface Methodology

In recent years, much attention has been paid to chitosan oligosaccharides (COS) because COS have shown physiological activities such as antitumor effect and antimicrobial activity.1 Compared with chitosan, chitosan oligosaccharides (COS) have some advantages such as water solubility, lower viscosities, lower molecular weights and shorter chain lengths. COS could be obtained from chitosan hydrolysis by chitosanase and this approach is popular by right of low production cost, low environmental impact and high reproducibility.2–3 Chitosanases (EC 3.2.1.132) are glycosyl hydrolases that catalyze the hydrolysis of β-(1→4) glycosidic bonds of chitosan to produce glucosamine oligosaccharides and the enzymes could be produced by bacteria, actinomycetes, and fungi.4–9 It is reported that most chitosanases are induced by substrates including powder chitosan and colloidal chitosan.10 Despite all of this, chitosanase is still unavailable in bulk quantities for commercial applications because of low enzymes productivity by chitosanolytic strains.11 Therefore, this problem could be resolved by isolating chitosanolytic strains with high chitosanase productivity, optimizing fermentation conditions for chitosanase production and reducing chitosanase production cost. Consequently, using cheaper natural substrates for chitosanase production is popular, as this approach not only improves chitosanase productivity, but also reduces chitosanase production cost. Shrimp shell is a kind of byproduct in seafood industries and it mainly contains chitin, chitosan and calcium carbonate. It can act as inducer and carbon source in the medium for chitosanase production. In the present study, with the use of response surface methodology (RSM), efforts were carried out to optimize chitosanase production by a newly isolated Aspergillus fumigatus YT-1 under submerged fermentation, while the mixture of shrimp shell powder and wheat bran was adopted in the medium. Furthermore, the optimal basic conditions for chitosan hydrolysis were preliminarily investigated.