Is chitin biodegradable in the environment?
Given the enormous amounts of chitin naturally produced each year, it is clear that very efficient chitin degradation must occur in nature. Also, chitin is a rich source for both carbon and nitrogen, making it an interesting substrate for micro-organisms to grow on. In fact, highly efficient chitin degrading bacteria are known both in terrestrial soils and in marine or soft water sludge. Typically, degradation of chitin containing biomaterials first requires the degradation of other substances such as glycans and proteins using suitable enzymes, to unmask the chitin. Enzymatic chitin degradation then begins with a combination of different chitinases, often supported by chitin binding proteins with chitin monooxygenase activity. These typically yield small chitin oligomers of a degree of polymerization of two and three (chitin dimer = chitobiose, chitin trimer = chitotriose) which are then further degraded to monomers by the action of N-acetylglucosaminidases. Alternatively, some bacteria partially de-N-acetylate the chitin oligomers by the use of chitin de-N-acetylases, typically yielding partially acetylated chitosan oligosaccharides which are then further degraded by N-acetylglucosaminidases and/or glucosaminidases, depending on the structure of the oligosaccharide which, in turn, depends on the on the mode of action of the deacetylating enzyme.