Analysis of symbiosis among microbes forcused on a thermophilic symbiotic bacterium

我们从以下两个方面分析了嗜热共生杆菌(ST)和芽孢杆菌S(BS)之间的绝对共生关系：(1)芽孢杆菌的pts1基因可能参与了共生关系。由于嗜热共生杆菌对嗜热共生杆菌的促生长活性很弱，我们已经从BS的细胞提取液中纯化了pts1蛋白。另一方面，我们注意到在培养基中添加葡萄糖完全抑制了ST的生长，但不能抑制BS的生长，进一步的实验表明，即使在培养基中有葡萄糖存在的情况下，pts1缺失的突变体也支持ST的生长。因此，我们初步假设BS对ST的促生长活性受分解代谢抑制的控制，PTSL参与BS细胞对分解代谢物的摄取，但不直接参与ST的支持活性。(Ii)ST在自然环境中的分布。通过广泛的筛选，我们已经假设ST广泛存在于自然生境中。同时，我们注意到ST经常从牛粪制成的堆肥中分离出来。进一步对几种草食动物的消化器官内容物进行筛选，结果表明ST是瘤胃细菌的一种可能性很高。这与ST的细胞和生理特征相吻合。

We have analyzed the absolute symbiosis between symbiobacterium thermophilum (ST) and Bacillus strain S (BS) from the following two aspects.(I) Possible involvement of ptsl gene of Bacillus in the symbiosis.We have previously purified Ptsl protein from the cell extract of BS following its very weak growth-supporting activity for ST.We have performed expression and purification of recombinant Ptsl protein by E.coli system, and failed to detect it's ST-supporting activity. On the other hand, we have noticed that addition of glucose in the media completely inhibitted the growth of ST but not of BS, and further experiments showed that ptsl-deficient mutant supports the growth of ST even in the presence of glucose in the media. Therefore, we tentatively hypothesize that the growth supporting activity for ST by BS is under the control of catabolite repression, and ptsl is involved in the uptake of catabolites into the BS cells but not directly in the ST-supporting activity.(II) Distribution of ST in the natural environment.We have already postulated that ST exists widely in the natural habitat through our extensive screening. Simultaniously, we noticed that ST is frequently isolated from composts made from bovine excreta. Further results of screening with contents of digestive organs of several herbivorus animals showed the high possibillity that ST is one of rumen bactera. It agrees with the cellular and physiological features of ST.