The fermentation of branched-chain amino acids (BCAAs) to branched-chain fatty acids (BCFAs) and branched-chain alcohols (BCOHs) is described using Thermoanaerobacter pseudoethanolicus. BCAAs were not degraded without an electron scavenging system but were degraded to a mixture of their BCFA (major) and BCOH (minor) when thiosulfate was added to the culture. Various environmental parameters were investigated using isoleucine as the substrate which ultimately demonstrated that at higher liquid–gas phase ratios the formation of 2-methyl-1-butanol from isoleucine achieved a maximal titer of 3.4 mM at a 1:1 liquid–gas ratio suggesting that higher partial pressure of hydrogen influences the BCOH/BCFA ratio but did not increase further with higher L–G phase ratios. Alternately, increasing the thiosulfate concentration decreased the BCOH to BCFA ratio. Kinetic monitoring of BCAA degradation revealed that the formation of BCOHs occurs slowly after the onset of BCFA formation. ¹³C2-labeled studies of leucine confirmed the production of a mixture of 3-methyl-1-butyrate and 3-methyl-1-butanol, while experiments involving ¹³C1-labeled 3-methyl-1-butyrate in fermentations containing leucine demonstrated that the carboxylic acid is reduced to the corresponding alcohol. Thus, the role of carboxylic acid reduction is likely of importance in the production of BCOH formation during the degradation of BCAA such as leucine.

中文翻译：

---

拟嗜热厌氧杆菌的支链氨基酸分解代谢揭示了形成支链醇的潜在途径。

使用嗜热厌氧嗜热杆菌描述了将支链氨基酸（BCAAs）发酵为支链脂肪酸（BCFA）和支链醇（BCOH）的过程。。在没有电子清除系统的情况下，BCAA不会降解，但是当将硫代硫酸盐添加到培养物中时，BCAA会降解为BCFA（主要）和BCOH（次要）的混合物。使用异亮氨酸作为底物对各种环境参数进行了研究，最终证明了在较高的液相-气相比下，异亮氨酸形成的2-甲基-1-丁醇在1：1的液-气比下的最大滴度为3.4 mM，这表明氢的较高分压会影响BCOH / BCFA比，但随着L-G相比的增加，氢的分压不会进一步增加。或者，增加硫代硫酸盐的浓度会降低BCOH与BCFA的比例。对BCAA降解的动力学监测表明，BCOH的形成是在BCFA形成开始后缓慢发生的。¹³C2标记的亮氨酸研究证实产生了3-甲基-1-丁酸酯和3-甲基-1-丁醇的混合物，而涉及¹³ C1标记的3-甲基-1-丁酸酯的发酵实验表明，亮氨酸羧酸还原为相应的醇。因此，羧酸还原的作用可能在诸如亮氨酸的BCAA降解过程中在BCOH形成的产生中很重要。