Institute of Modern Physics, Chinese Academy of Sciences, 509 Nanchang Road, Lanzhou, Gansu 730000, PR China.
China Pharmaceutical University, #24 Tongjiaxiang, Nanjing 210009, PR China.
Biotechnol Biofuels. 2014 Feb 18;7(1):22. doi: 10.1186/1754-6834-7-22.
Butyric acid as a renewable resource has become an increasingly attractive alternative to petroleum-based fuels. Clostridium tyrobutyricum ATCC 25755T is well documented as a fermentation strain for the production of acids. However, it has been reported that butyrate inhibits its growth, and the accumulation of acetate also inhibits biomass synthesis, making production of butyric acid from conventional fermentation processes economically challenging. The present study aimed to identify whether irradiation of C. tyrobutyricum cells makes them more tolerant to butyric acid inhibition and increases the production of butyrate compared with wild type.
In this work, the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 3.6, 7.2 and 10.8 g·L-1 equivalents were studied. The results showed that, regardless of the irradiation used, there was a gradual inhibition of cell growth at butyric acid concentrations above 10.8 g·L-1, with no growth observed at butyric acid concentrations above 3.6 g·L-1 for the wild-type strain during the first 54 h of fermentation. The sodium dodecyl sulfate polyacrylamide gel electrophoresis also showed significantly different expression levels of proteins with molecular mass around the wild-type and irradiated strains. The results showed that the proportion of proteins with molecular weights of 85 and 106 kDa was much higher for the irradiated strains. The specific growth rate decreased by 50% (from 0.42 to 0.21 h-1) and the final concentration of butyrate increased by 68% (from 22.7 to 33.4 g·L-1) for the strain irradiated at 114 AMeV and 40 Gy compared with the wild-type strains.
This study demonstrates that butyric acid production from glucose can be significantly improved and enhanced by using 12C6+ heavy ion-irradiated C. tyrobutyricum. The approach is economical, making it competitive compared with similar fermentation processes. It may prove useful as a first step in a combined method employing long-term continuous fermentation of acid-production processes.
丁酸作为一种可再生资源，已经成为一种越来越有吸引力的石油基燃料替代品。产丁酸梭菌 ATCC 25755T 是一种生产酸的发酵菌株，已有大量文献记载。然而，据报道，丁酸会抑制其生长，而乙酸的积累也会抑制生物量的合成，因此从传统发酵工艺生产丁酸在经济上具有挑战性。本研究旨在确定辐照丁酸梭菌细胞是否会使其对丁酸抑制更具耐受性，并与野生型相比增加丁酸的产量。
在这项工作中，研究了经典适应生长在 3.6、7.2 和 10.8 g·L-1 等当量下的丁酸梭菌培养物的发酵动力学。结果表明，无论使用哪种辐照，丁酸浓度高于 10.8 g·L-1 时，细胞生长都会逐渐受到抑制，野生型菌株在前 54 h 的发酵过程中，丁酸浓度高于 3.6 g·L-1 时，细胞不再生长。十二烷基硫酸钠聚丙烯酰胺凝胶电泳也显示出野生型和辐照菌株的蛋白质表达水平存在显著差异。结果表明，辐照菌株的分子量约为 85 和 106 kDa 的蛋白质比例要高得多。与野生型菌株相比，辐照强度为 114 AMeV 和 40 Gy 的菌株的比生长速率降低了 50%（从 0.42 降至 0.21 h-1），丁酸的最终浓度提高了 68%（从 22.7 升至 33.4 g·L-1）。
本研究表明，通过使用 12C6+重离子辐照丁酸梭菌，可以显著提高和增强葡萄糖生产丁酸的能力。该方法经济实惠，与类似的发酵工艺相比具有竞争力。它可能在采用长期连续发酵酸生产工艺的联合方法中作为第一步是有用的。
