Abstract:

Chitin, a linear homo-polysaccharides composed of N-acetylglucosamine (GlcNAc) through β-1,4-glycosidic bonds, is the richest nitrogen containing biomass resource on earth, with an annual production of 10 billion tonnes. Chitin is widely distributed in nature, mainly found in the shells of shrimps and crabs, the exoskeletons of insects, and the cell walls of fungi. Due to its abundance and renewablity, especially the presence of the valuable nitrogen element, chitin receives widespread attention. However, the abundant hydrogen bonds in the structure of chitin and its huge molecular weight make it highly crystalline and insoluble in water, which leads to challenges in its degradation and high-value utilization. Thus, chitin resource is often discarded as wastes or buried, leading to serious environment issues and wasted resources. Conversion of abundant chitin resources into high value-added chemicals has both environmental and economic significance. Nowadays, the utilization of chitin resources is mainly done by efficient, low-cost chemical method, but there is huge environmental pollution. Compared with chemical method, the biological method shows great potential in the context of green and sustainable development due to the advantages of environmentally friendly process and mild reaction conditions. In this review, the sources and classifications, catalytic mechanisms and properties of key enzymes are introduced. Secondly, the current status of chitin bio-degradation to monosaccharides (GlcNAc and glucosamine) and oligosaccharides (N-acetyl chitooligosaccharides and chitooligosaccharides), and further bio-converted into nitrogen-containing chemicals are reviewed. Although more studies on enzymes involving chitin degradation and conversion have been carried out and obtained certain achievements. However, the diversity and complexity of these enzymes, coupled with the low activity and secretory nature and other factors, have hindered the real industrial chitin degradation and conversion. Consequently, the challenges in bio-degradation and high-value conversion process of chitin such as low activity of enzyme, poor efficiency and high cost are highlighted. Finally, the important role of rapidly developing synthetic biology technologies in chitin utilization is envisaged, which will aid the efficient bio-refining of chitinous resources.

Key words: chitin, biological degradation, chitinolytic enzyme, biological transformation, nitrogen-containing chemicals

摘要：

几丁质是由N-乙酰氨基葡萄糖（GlcNAc）通过β-1，4-糖苷键构成的高分子聚合物，是地球上储量最丰富的含氮生物质资源，在自然界分布广泛，主要存在于虾蟹外壳、昆虫外骨骼和真菌细胞壁中。由于几丁质含量巨大、可再生，特别是含有珍贵的氮元素，其资源化利用一直受到广泛关注。然而几丁质结构中丰富的氢键作用力与巨大的分子量，赋予了其高结晶度和不溶于水的特性，导致其降解和高值化利用受到挑战，因此常被作为垃圾丢弃或掩埋，污染环境的同时浪费资源。在几丁质降解利用的众多方法中，生物法因过程环保、反应条件温和等优点，在绿色可持续发展的大背景下展现出巨大潜力。本文首先系统介绍了自然界中催化几丁质降解关键酶的来源与分类、催化机制及特性。其次综述了生物法降解几丁质为单糖（GlcNAc和氨基葡萄糖）和寡糖（几丁寡糖和壳寡糖），以及进一步生物转化合成含氮化合物的现状。最后阐述了几丁质生物降解和高值转化过程中所面临的几丁质降解与转化酶活性低、效率差及成本高昂等诸多挑战，展望了发展迅速的合成生物学技术在几丁质生物转化中的重要作用，这将为几丁质资源的高效生物炼制提供助力。

关键词: 几丁质, 生物降解, 几丁降解酶, 生物转化, 含氮化学品