One-step processing of shrimp shell waste with a chitinase fused to a carbohydrate-binding module

As a potential renewable and nitrogen-rich feedstock, tons of shrimp shell wastes are generated from the increasing consumption of seafood. However, its traditional processing is costly and creates pollution. The bioconversion of shell waste into valuable nitrogen-containing chemicals via enzymatic hydrolysis is a promising technology. However, intact shells are poorly hydrolyzed by chitinases unless pre-demineralization and deproteinization with chemicals or proteases is performed. In this study, three carbohydrate-binding modules (CBMs) were fused to the C-terminal of chitinase Chit46 to enhance its hydrolysis of shrimp shell wastes. The addition of CBMs significantly improved the chitinase activity and substrate-binding activity of Chit46. Chimeric chitinases could directly hydrolyze shrimp shells without pretreatment and their hydrolysis efficiency was much higher than previously reported chitinases. With the modified chitinase (‘Chit46-CBM3’), we developed a one-step shrimp shell processing method. The method could convert 46.5% of chitin in shrimp shell to chitin oligomers by hydrolysis in 12 h. Partial protein release accompanied chitin hydrolysis. Consisted of 8.8 g/l chitin oligomers and 11.3 g/l protein, the hydrolysate could support robust microbial growth and the residue was more digestible by mammals than conventional shrimp shell powder. This process is superior to previously reported methods in cost, conversion efficiency and labour. The one-step process also exhibited a much lower ecological footprint than conventional processing and can be applied to other chitinous wastes in addition to shrimp shells.