白蚁及共生微生物木质纤维素水解酶的种类
Lignocellulolytic enzymes in termite and its symbiotic microbes
相 辉,周志华**
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作者单位：中国科学院上海植物生理生态研究所 上海 200032
中文关键词：白蚁; 原生动物; 真菌;细菌; 纤维素水解酶
英文关键词：termite, symbiotic flagellate, fungi, bacteria, lignocellulolytic enzymes
中文摘要：白蚁是热带生态系统重要的木质纤维素降解者。白蚁种类丰富，可分成高等白蚁和低等白蚁，食性也具有各自特点。白蚁自身可以产生纤维素酶，主要是GHF9的内切葡聚糖酶（EG），也有β-葡萄糖苷酶（GB）。低等白蚁共生的原虫中已发现丰富的纤维素酶基因，属于GHF5，7和45。同时还有其他相关功能基因，如木聚糖酶和果胶类物质水解酶。高等白蚁肠道中没有共生原虫。高等培菌白蚁可以利用共生蚁巢伞属真菌促进木质纤维素降解，真菌可以产生纤维素酶，果胶质水解酶类、木聚糖酶，同时还产生可能与木质素分解相关的一种漆酶,但是从分子水平，关于共生真菌纤维素水解酶的研究还较少。白蚁肠道已分离出许多具有木质纤维素降解能力的菌株，最近的研究也发现了大量细菌纤维素酶基因。白蚁-共生系统丰富的木质纤维素水解酶类为发展生物方法开发纤维素乙醇这一思路提供有价值的资源。
英文摘要：Termites are important decomposers of lignocellulose in tropical ecosystems. They comprise a complex assemblage of diverse species, roughly divided into so-called lower and higher termites with different phagous characters. Termites can produce their own endoglucanases（EG）of GHF9, as well as glucosidase. Protistan symbiotic system of lower termite degrades cellulosic compounds with high efficiency. Diverse lignocellulolytic enzymes are found in this system including GHF5, 7 and 45. Other related functional genes may include xylanase and pectinolytic related enzymes. Higher termites don't harbor flagellate. Fungus-growing termites efficiently decompose lignocellulose through their symbiotic relationship with basidiomycete fungi of the genus Termitomyces. The symbiotic fungi produce cellulose, xylanase and putative pectinolytic enzymes. They also produce laccase which might be related to lignin degradation. However, on molecular level, studies on lignocellulolytic emzymes of symbiotic fungi are relatively few. Many lignocellulolytic bacteria strains were isolated from termite guts, divers cellulose genes were also found recently. Lignocellulolytic enzymes in termite and its symbiotic systems may have potentials for the idea of cellulosic ethanol production by biological process.