An ecological study on the tryptophan synthesis by rumen protozoa

本研究的主要目的是了解瘤胃原生动物在瘤胃微生物生态系统中对色氨酸合成的影响程度。1990年首先检测了原生动物悬浮液(P)的trp合成能力，1991年检测了细菌悬浮液(B)的trp合成能力进行比较，1992年检测了原生动物和细菌混合悬浮液（BP）的trp合成能力，以了解其总量。本研究以吲哚乙酸酯（IAA）和吲哚乙酸酯（IPA）为底物，并对这些化合物产生的除色氨酸外的一些代谢产物进行了研究。我们将在这里特别报道在三年的研究期间关于色氨酸合成的结果相互比较。P孵育12 h后，IPA （1mM）转化为色氨酸约12%，色氨酸在培养基中积累。磷合成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^<14>C-IPA来演示合成色氨酸，但没有任何公司生产，我们放弃了。在P中，IAA不产生色氨酸。在B和BP中，Trp积累较少，因为它们是生长体系。在这些体系中，色氨酸合成用^<14>C-IAA测定。孵育12 h后，B细菌蛋白中明显检测到放射性色氨酸，估计色氨酸含量为5.7 nmol/ml。这意味着在b中发生了IAA的还原羧化生成IPA和IPA的连续转氨化生成色氨酸。在BP的微生物蛋白中也检测到放射性色氨酸，其量为10.4 nmol/ml，比b中高出约80%。由此可见，原生动物似乎通过其特有的转氨能力刺激BP中色氨酸的合成。细菌对IAA的还原羧化速度似乎响应原生动物和细菌对IPA的转氨化速度。

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.