Kudo T, Ohkuma M, Moriya S, Noda S, Ohtoko K
Institute of Physical and Chemical Research (RIKEN), Saitama, Japan.
Extremophiles. 1998 Aug;2(3):155-61. doi: 10.1007/s007920050055.
A termite maintains an anaerobic microbial community in its hindgut, which seems to be the minimum size of an anaerobic habitat. This microbial community consists of bacteria and various anaerobic flagellates, and it is established that termites are totally dependent on the microbes for the utilization of their food. The molecular phylogenetic diversity of the intestinal microflora of a lower termite, Reticulitermes speratus, was examined by a strategy that does not rely on cultivation of the resident microorganisms. Small subunit ribosomal RNA (ssrRNA) genes were directly amplified from the mixed-population DNA of the termite gut by polymerase chain reaction (PCR) and clonally isolated. Most sequenced clones were phylogenetically affiliated with the four major groups of the domain Bacteria: the Proteobacteria group, the Spirochete group, the Bacteroides group, and the Low G + C gram-positive bacteria. The 16S rRNA sequence data show that the majority of the intestinal microflora of the termite consists of new species that are yet to be cultured. The phylogeny of a symbiotic methanogen inhabiting the gut of a lower termite (R. speratus) was analyzed without cultivation. The nucleotide sequence of the ssrDNA and the predicted amino acid sequence of the mcrA product were compared with those of the known methanogens. Both comparisons indicated that the termite symbiotic methanogen belonged to the order Methanobacteriales but was distinct from the known members of this order. The diversity of nitrogen-fixing organisms was also investigated without culturing the resident microorganisms. Fragments of the nifH gene, which encodes the dinitrogenase reductase, were directly amplified from the mixed-population DNA of the termite gut and were clonally isolated. The phylogenetic analysis of the nifH amino acid sequences showed that there was a remarkable diversity of nitrogenase genes in the termite gut. The molecular phylogeny of a symbiotic hypermastigote Trichonympha agilis (class Parabasalia; order Hypermastigida) in the hindgut of R. speratus was also examined by the same strategy. The whole-cell hybridization experiments indicated that the sequence originated from a large hypermastigote in the termite hindgut, Trichonympha agilis. According to the phylogenetic trees constructed, the hypermastigote represented one of the deepest branches of eukaryotes. The hypermastigote along with members of the order Trichomonadida formed a monophyletic lineage, indicating that the hypermastigote and trichomonads shared a recent common ancestry.
白蚁在其后肠维持着一个厌氧微生物群落，这似乎是厌氧栖息地的最小规模。这个微生物群落由细菌和各种厌氧鞭毛虫组成，并且已经确定白蚁在食物利用方面完全依赖这些微生物。通过一种不依赖于培养驻留微生物的策略，对白蚁（黄胸散白蚁）肠道微生物群的分子系统发育多样性进行了研究。从小亚基核糖体RNA（ssrRNA）基因通过聚合酶链反应（PCR）直接从白蚁肠道的混合群体DNA中扩增，并进行克隆分离。大多数测序克隆在系统发育上与细菌域的四大类相关：变形菌门、螺旋体门、拟杆菌门和低G + C革兰氏阳性菌。16S rRNA序列数据表明，白蚁肠道微生物群的大多数由尚未培养的新物种组成。对白蚁（黄胸散白蚁）肠道中一种共生产甲烷菌的系统发育进行了无需培养的分析。将ssrDNA的核苷酸序列和mcrA产物的预测氨基酸序列与已知产甲烷菌的序列进行了比较。两种比较都表明，白蚁共生产甲烷菌属于甲烷杆菌目，但与该目的已知成员不同。还在不培养驻留微生物的情况下研究了固氮生物的多样性。编码二氮酶还原酶的nifH基因片段直接从白蚁肠道的混合群体DNA中扩增并克隆分离。对nifH氨基酸序列的系统发育分析表明，白蚁肠道中存在显著的固氮酶基因多样性。还通过相同策略对白蚁（黄胸散白蚁）后肠中一种共生超鞭毛虫（副基体纲；超鞭毛目）敏捷全毛虫的分子系统发育进行了研究。全细胞杂交实验表明该序列源自白蚁后肠中的一种大型超鞭毛虫，敏捷全毛虫。根据构建的系统发育树，超鞭毛虫代表了真核生物最深的分支之一。超鞭毛虫与毛滴虫目成员形成了一个单系谱系，表明超鞭毛虫和毛滴虫有最近的共同祖先。
