An ecological study on the tryptophan synthesis by rumen protozoa

本研究的主要目的是了解在何种程度上瘤胃原虫可以发挥作用的色氨酸（Trp）的合成在瘤胃微生态系统。1990年首先测定了原生动物悬液（P）的色氨酸降解能力，1991年测定了细菌悬液（B）的色氨酸降解能力，以作比较，1992年测定了原生动物和细菌混合悬液（BP）的色氨酸降解能力，以了解总量。以吲哚丙酮酸（IPA）和吲哚乙酸（IAA）为底物，研究了这些化合物产生的Trp以外的代谢产物。我们将在这里特别报告的结果有关色氨酸合成在三年的研究期间相互比较。培养12 h后，IPA（1 mM）转化为Trp的转化率约为12%，Trp在培养基中积累。P中的色氨酸通常以这种方式在培养基中积累，因为原生动物不能在这种培养基中生长。我们计划用^ C-IPA来演示色氨酸的合成<14>，但没有任何公司生产，我们放弃了。在P中，IAA不产生Trp。在B和BP中，Trp没有积累这么多，因为这些是生长系统。在这些系统中，使用13 C-IAA检查Trp合成<14>。孵育12 h后，B中的菌体蛋白中明显检测到放射性色氨酸，其含量估计为5.7 nmol/ml。这意味着在B中发生IAA还原羧化生成IPA和IPA连续转氨生成Trp。在细菌蛋白中也检测到放射性色氨酸，含量为10.4 nmol/ml，比B高80%。因此，原生动物似乎通过其特有的转氨能力刺激BP中Trp的合成。细菌对IAA还原羧化的速率似乎与细菌和原生动物对IPA转氨的速率相对应。

The main aim of the present study was to know to what extent rumen protozoa could play a role in tryptophan (Trp) synthesis in the rumen microbial ecosystem. In 1990 Trp-synthsizing ability of protozoal suspension (P) was examined at first, then in 1991 that of bacterial suspension (B) for comparison, and in 1992 that in mixed suspension of protozoa and bacteria (BP) was examined to know a total quantity. Indolepyruvate (IPA) and indoleacetate (IAA) were used as substrates in these study and some metabolites besides Trp produced from these compounds were also examined. We will report here especially the results concerning Trp synthesis during a three-year research period comparing each other. After 12 h incubation of P, IPA (1mM) was converted to Trp by about 12% and Trp accumulated in the medium. Trp synthsized in P usually accumulates in the medium in this way, because protozoa cannot grow in this medium. We planned to demonstrate the synthesis of Trp using ^<14>C-IPA, but it was not produced in any company, and we gave it up. In P, there was no production of Trp from IAA. In B and BP, Trp was not accumulated so much, because these were growing systems. In these systems, Trp synthesis was examined using ^<14>C-IAA. After 12 h incubation, radioactive Trp was obviously detected in bacterial protein in B and the amount was estimated to be 5.7 nmol/ml. This means an occurrence of a reductive carboxylation of IAA to produce IPA and a consecutive tranamination of IPA to produce Trp in B. Radioacitve Trp was also detected in microbial protein in BP and the amount was 10.4 nmol/ml which was about 80% higher than that in B. Thus protozoa seemed to stimulate Trp synthesis in BP by means of transaminating ability characteristic to them. The velocity of reductive carboxylation of IAA by bacteria seemed to respond to that of transamination of IPA by both protozoa and bacteria.