Identification of factors involved in the growth of Symbiobacterium thermophilum

嗜热共生杆菌最初是作为一种共生菌分离出来的，需要联合芽孢杆菌S菌株的支持才能生长。尽管嗜热链霉菌的完全生长需要与芽孢杆菌混合培养，但在含有酵母膏和胰蛋白胨的营养发酵液中没有芽孢杆菌的情况下，生长有限，低于1×10~(-7)个/毫升。在木炭处理的酵母膏和胰蛋白内酯-蛋白内酯中分别检测到两种支持独立生长的活性。用Rb~(++)、NH_4~(2+)等一价阳离子和CO_2、碳酸氢盐、氰酸酯、草酰乙酸酯等几种与羧基酶和碳酸氢酶催化反应有关的化合物取代炭化酵母抽提物的活性。酪蛋白或肌红蛋白经胰酶消化后，活性分布在不同分子大小的多肽中，取代了胰蛋白内酯-蛋白内酯的活性。除了这些因素和有限独立生长所需的无菌条件外，在大量新鲜培养基上透析培养释放了限制，使其在无菌培养中完全生长超过1×10^9细胞/毫升。因此，对自身代谢产物的高度敏感性是嗜热链霉菌共生特性的另一个关键。嗜热链霉菌细胞脂肪酸中的支链异C17和反C17脂肪酸对其生长有明显的抑制作用，提示它们可能参与了嗜热链霉菌的自限生长。我们得出结论，嗜热链霉菌的共生生长是由芽孢杆菌提供的双重功能支持的，一种是提供复杂的生长因子，另一种是从培养物中去除抑制代谢产物。

Symbiobacterium thermophilum was originally isolated as a symbiotic bacterium requiring support of the associating Bacillus strain S for growth. Although full growth of S. thermophilum needs mixed culture with the bacillus, limited growth of less than 1 x 10^7 cells/ml was found to occur in the absence of the bacillus in nutrient broth containing yeast extract and tryptone-peptone. Two types of the activity to support the independent growth were detected in charcoal-treated yeast extract and tryptone-peptone, respectively. The activity in charcoal-treated yeast extract was replaced by monovalent cations such as Rb^+, and NH_4^+, and several compounds such as CO_2, bicarbonate, cyanate and oxaloacetate, which are related to the reactions catalyzed by carboxylase and carbonic anhydrase. The activity in tryptone-peptone was replaced by the tryptic digest of casein or myoglobin, in which the activity distributed in peptides of various molecular sizes. In addition to these factors as well as anaereobic condition required for the limited independent growth, dialysis culture against a large volume of fresh medium released the limitation to achieve the full growth exceeding 1 x 10^9 cells/ml in the axenic culture. Thus hyper-sensitivity to the own metabolites was indicated as another key of the symbiotic characteristics of S. thermophilum. Branched iso-C17 and anteiso-C17 fatty acids, components of cellular fatty acids of S. thermophilum, caused potent growth inhibition, suggesting their possible involvement in the self-limited growth. We conclude that symbiotic growth of S. thermophilum is supported by the dual functions offered by Bacillus, one providing the complex growth factors and the other to remove the inhibitory metabolites from the culture.