低等白蚁肠道共生微生物的多样性及其功能

Diversity and function of symbiotic microbes in the gut of lower termites

低等白蚁肠道里存在着复杂的微生物区系,包括真核微生物鞭毛虫和原核生物,细菌及古细菌。低等白蚁的后肠以特别膨大的囊形胃及其氢氧浓度的明显梯度分布和丰富的微生物区系为特征,是白蚁进行木质纤维素消化的主要器官。后肠内的鞭毛虫能将纤维素水解并发酵为乙酸,二氧化碳和氢,为白蚁提供营养和能源。系统发育研究表明,低等白蚁肠道共生细菌的主要类群为白蚁菌群1、螺旋体、拟杆菌,低G+C mol%含量的革兰氏阳性菌和紫细菌等。而古细菌主要为甲烷短杆菌属的产甲烷菌。共生原核生物与二氧化碳的还原和氮的循环等代谢有关。但肠道共生微生物的具体功能和作用机制还有待进一步的揭示。

The gut of lower termites harbor a complex microbial community, including eukaryotic flagellates and prokaryotic bacteria and archaea, which play important roles in the wood-cellulose digestion of these termites, The hindguts of lower termites are characterized with an enlarged paunch with steep oxygen and hydrogen gradient and not randomly distributed abundant microorganisms, The symbiotic flagellates in the gut of lower termites, which are normally associated with epibionts or endobionts, are phylogenetically affiliated with Trichomonadida, Hypermastigida and Oxymonadida, They endocytose wood particles and ferment the polysaccharide components to acetate, CO2 and H2, which are further metabolized by symbiotic prokaryotes as energy and nutrition sources in the termites. Cellulose genes such as glycosyl hydrolase family 45 have been identified in gut protists with molecular approach. Phylogenetic analysis have revealed that in the gut of lower termites, such as several Reticulitermites species, most of the dominant bacteria belong to phyla like ＂Termite group 1＂, Spirochaetes, Firmicutes, Bacteroidetes, and Proteobacteria. These bacteria clones normally form distinct termite clusters in phylogenetic trees, which show the existence of specific microbial diversity in the termite guts. Most of the symbiotic archaea in the gut of lower termites are methanogens and affiliated with the genus Methanobrevibacter by phylogenetic analysis and pure culture. The symbiotic bacteria and archaea may involve in the reduction of CO2 and the metabolism of N2 in these termite guts. However, the functions and metabolic mechanisms of the symbiotic flagellates and prokaryotes in the gut of lower termites are still remaining to be further elucidated.