Zheng Hang, Zeng Raymond J, Duke Mikel C, O'Sullivan Cathryn A, Clarke William P
Centre for Solid Waste Bio-Processing, Schools of Civil and Chemical Engineering, The University of Queensland, Brisbane, 4072, Queensland, Australia.
Biotechnol Bioeng. 2015 Jun;112(6):1177-86. doi: 10.1002/bit.25525. Epub 2015 Apr 18.
It is well established that metabolic pathways in the fermentation of organic waste are primarily controlled by dissolved H2 concentrations, but there is no reported study that compares observed and predicted shifts in fermentation pathways induced by manipulating the dissolved H2 concentration. A perfusion system is presented that was developed to control dissolved H2 concentrations in the continuous fermentation of glucose by a culture highly enriched towards Thermoanaerobacterium thermosaccharolyticum (86 ± 9% relative abundance) from an originally diverse consortia in the leachate of a laboratory digester fed with municipal solid waste. Media from a 2.5 L CSTR was drawn through sintered steel membrane filters to retain biomass, allowing vigorous sparging in a separate chamber without cellular disruption. Through a combination of sparging and variations in glucose feeding rate from 0.8 to 0.2 g/L/d, a range of steady state fermentations were performed with dissolved H2 concentrations as low as an equivalent equilibrated H2 partial pressure of 3 kPa. Trends in product formation rates were simulated using a H2 regulation partitioning model. The model correctly predicted the direction of products redistribution in response to H2 concentration changes and the acetate and butyrate formation rates when H2 concentrations were less than 6 kPa. However, the model over-estimated acetate, ethanol and butanol productions at the expense of butyrate production at higher H2 concentrations. The H2 yield at the lowest dissolved H2 concentration was 2.67 ± 0.08 mol H2 /mol glucose, over 300% higher than the yield achieved in a CSTR operated without sparging.
众所周知，有机废物发酵中的代谢途径主要受溶解氢浓度控制，但尚无研究报道比较通过控制溶解氢浓度诱导的发酵途径的观察到的和预测的变化。本文介绍了一种灌注系统，该系统用于在葡萄糖连续发酵过程中控制溶解氢浓度，发酵所用培养物是从以城市固体废物为进料的实验室消化池渗滤液中最初多样的菌群中高度富集嗜热栖热放线菌（相对丰度为86±9%）而获得的。将来自2.5L连续搅拌釜式反应器（CSTR）的培养基通过烧结钢膜过滤器抽出以保留生物质，从而允许在单独的腔室中进行剧烈鼓泡而不破坏细胞。通过鼓泡和将葡萄糖进料速率从0.8g/L/d变化到0.2g/L/d的组合，进行了一系列稳态发酵，溶解氢浓度低至相当于3kPa的平衡氢分压。使用氢调节分配模型模拟了产物形成速率的趋势。该模型正确预测了响应氢浓度变化时产物重新分布的方向以及氢浓度小于6kPa时乙酸盐和丁酸盐的形成速率。然而，在较高氢浓度下，该模型高估了乙酸盐、乙醇和丁醇的产量，而牺牲了丁酸盐的产量。最低溶解氢浓度下的氢产率为2.67±0.08mol H2/mol葡萄糖，比无鼓泡操作的CSTR中实现的产率高出300%以上。
