The Termite-Symbionts System

白蚁与细菌、原生动物和真菌具有共生关系，它们成功地利用了死亡植物的细胞壁成分，其中含有地球上最丰富的有机质纤维素，但只含有少量的氮素。本国际合作研究项目旨在阐明“白蚁-共生系统”，特别涉及(1)纤维素分解过程和氮素获取，(2)白蚁的环境因素和生态特性促进白蚁从低级白蚁向高级白蚁的宏观演化，(3)白蚁在泰国、澳大利亚和日本陆地生态系统氮流中的作用。最重要的问题和答案如下：1)为什么食木性白蚁能够以含氮量很少的食物为生？食木性白蚁体内30%至50%的氮来自大气氮2)谁产生纤维素酶？在低等白蚁中，纤维素酶是由原生动物(在后肠)和自己(在唾液腺和中肠)产生的，而在高等白蚁中，纤维素酶是由自己(在中肠)产生的。3)谁分解半纤维素？在低等白蚁中，分解半纤维素的酶是由原生动物和白蚁自己产生的。4)哪些因素促进了白蚁的宏观进化？在对澳大利亚热带森林和邻近桉树稀树草原白蚁生物学进行比较研究的基础上，提出了“木质素覆盖假说”，认为白垩纪(湿润到干燥)的气候变化以及白蚁筑巢地点和食物的变化具有重要意义。

The termites, who have symbiotic relationship with bacteria, protozoa and fungi, have succeeded in utilizing cell-wall component of dead plants, which contains cellulose, the most abundant organic matter on the earth, but contains only a little nitrogen.The present international cooperative research project intends to clarify the "Termite-Symbionts System" with special reference to (1) cellulose decomposition process and nitogen acquisition, (2) environmental factors and ecological traits of termites promoting the macroevolution in termites from lower to higher termites, and (3) the role of termites in nitrogen flow of terrestrial ecosystems in Thailand, Australia and Japan. Most important questions and answers are as follows.1) Why are xylophagous termites able to subsist on a diet containing very little nitrogen? Thirty to fifty percent of nitrogen of bodies of a xylophagous termite (Neotermes koshunensis, Kalotermitidae) come from atmospheric nitrogen.2) Who produce cellulases? In lower termites (Reticulitermes speratus) cellulases are produced by protozoa (in hind gut) and by themselves (in salivary gland and midgut), while in higher termites cellulases are produced by themselves (in midgut).3) Who decompose hemicellulose? In a lower termite (Reticulitermes speratus), enzymes to decompose hemicellulose are produced by protozoa and termites themselves.4) What kind of factors have promoted the macroevolution in termites? Based on comparative studies on biology of termites in reinforests and adjacent Eucalyptus savanna in Australia, 'Lignin cover hypothesis' was proposed, suggesting the importance of climatic change in Cretaceous period (moist to dry) as well as the change in nest site and food of termites.