Ato Makoto, Ishii Masaharu, Igarashi Yasuo
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, The University of Graduate School of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Department of Biotechnology, Graduate School of Agriculture and Life Sciences, The University of Graduate School of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
J Biosci Bioeng. 2014 Aug;118(2):160-5. doi: 10.1016/j.jbiosc.2014.02.003. Epub 2014 Mar 11.
In anaerobic condition, amino acids are oxidatively deaminated, and decarboxylated, resulting in the production of volatile fatty acids. In this process, excess electrons are produced and their consumption is necessary for the accomplishment of amino acid degradation. In this study, we anaerobically constructed leucine-degrading enrichment cultures from three different environmental samples (compost, excess sludge, and rice field soil) in order to investigate the diversity of electron-consuming reaction coupled to amino acid oxidation. Constructed enrichment cultures oxidized leucine to isovalerate and their activities were strongly dependent on acetate. Analysis of volatile fatty acids (VFAs) profiles and community structure analysis during batch culture of each enrichment indicated that Clostridium cluster I coupled leucine oxidation to acetate reduction in the enrichment from the compost and the rice field soil. In these cases, acetate was reduced to butyrate. On the other hand, Clostridium cluster XIVb coupled leucine oxidation to acetate reduction in the enrichment from the excess sludge. In this case, acetate was reduced to propionate. To our surprise, the enrichment from rice field soil oxidized leucine even in the absence of acetate and produced butyrate. The enrichment would couple leucine oxidation to reductive butyrate synthesis from CO2. The coupling reaction would be achieved based on trophic link between hydrogenotrophic acetogenic bacteria and acetate-reducing bacteria by sequential reduction of CO2 and acetate. Our study suggests anaerobic degradation of amino acids is achieved yet-to-be described reactions.
在厌氧条件下，氨基酸发生氧化脱氨和脱羧反应，生成挥发性脂肪酸。在此过程中会产生过量电子，而消耗这些电子对于氨基酸降解的完成是必要的。在本研究中，我们从三种不同的环境样品（堆肥、剩余污泥和稻田土壤）中厌氧构建了降解亮氨酸的富集培养物，以研究与氨基酸氧化偶联的电子消耗反应的多样性。构建的富集培养物将亮氨酸氧化为异戊酸，其活性强烈依赖于乙酸盐。对每种富集培养物的分批培养过程中的挥发性脂肪酸（VFA）谱分析和群落结构分析表明，在来自堆肥和稻田土壤的富集培养物中，梭菌属第一簇将亮氨酸氧化与乙酸盐还原偶联。在这些情况下，乙酸盐被还原为丁酸盐。另一方面，在来自剩余污泥的富集培养物中，梭菌属第十四簇b将亮氨酸氧化与乙酸盐还原偶联。在这种情况下，乙酸盐被还原为丙酸盐。令我们惊讶的是，来自稻田土壤的富集培养物即使在没有乙酸盐的情况下也能氧化亮氨酸并产生丁酸盐。该富集培养物可能将亮氨酸氧化与由二氧化碳进行的还原性丁酸盐合成偶联。这种偶联反应可能是基于氢营养型产乙酸细菌和乙酸盐还原细菌之间的营养联系，通过二氧化碳和乙酸盐的顺序还原实现的。我们的研究表明，氨基酸的厌氧降解是通过尚未描述的反应实现的。
