Dept. of Bioengineering, Rice University, Houston, TX 77005, USA.
Biotechnol Prog. 2011 Sep-Oct;27(5):1225-31. doi: 10.1002/btpr.641. Epub 2011 Jun 16.
This work aimed to identify the key operational factors that significantly affect succinate production by the high succinate producing Escherichia coli strain SBS550MG (pHL413), which bears mutations inactivating genes adhE ldhA iclR ackpta::Cm(R) and overexpresses the pyruvate carboxylase from Lactococcus lactis. The considered factors included glucose concentration, cell density, CO(2) concentration in the gas stream, pH, and temperature. The results showed that high glucose concentrations inhibited succinate production and that there is a compromise between the total succinate productivity and succinate specific productivity, where the total productivity increased with the increase in cell density and the specific productivity decreased with cell density, probably due to mass transfer limitation. On the other hand, a CO(2) concentration of 100% in the gas stream showed the highest specific succinate productivity, probably by favoring pyruvate carboxylation, increasing the OAA pool that later is converted into succinate. A full factorial design of experiments was applied to analyze the pH and temperature effects on succinate production in batch bioreactors, where succinate yield was not significantly affected by either temperature (37 to 43°C) or pH (6.5 to 7.5). Additionally, the temperature effect on succinate productivity and titer was not significant, in the range tested. On the other hand, a pH of 6.5 showed very low productivity, whereas pH values of 7.0 and 7.5 resulted in significantly higher specific productivities and higher titers. The increase on pH value from 7.0 to 7.5 did not show significant improvement. Then, pH 7.0 should be chosen because it involves a lower cost in base addition.
本工作旨在确定关键操作因素，这些因素会显著影响具有突变的高琥珀酸产生大肠杆菌菌株 SBS550MG(pHL413)的琥珀酸生产，该突变使 adhE、ldhA、iclR 和 ackpta::Cm(R)失活，并过表达来自乳球菌 lactis 的丙酮酸羧化酶。所考虑的因素包括葡萄糖浓度、细胞密度、气流中的 CO2 浓度、pH 值和温度。结果表明，高葡萄糖浓度会抑制琥珀酸的产生，总琥珀酸生产力和琥珀酸比生产力之间存在折衷，总生产力随着细胞密度的增加而增加，比生产力随着细胞密度的增加而降低，可能是由于质量传递限制。另一方面，气流中 100%的 CO2 浓度显示出最高的琥珀酸比生产力，这可能是通过有利于丙酮酸羧化，增加 OAA 池，进而转化为琥珀酸。采用完全析因实验设计分析了批式生物反应器中 pH 值和温度对琥珀酸生产的影响，其中琥珀酸产率不受温度（37 至 43°C）或 pH 值（6.5 至 7.5）的显著影响。此外，在所测试的范围内，温度对琥珀酸生产力和浓度的影响不显著。另一方面，pH 值为 6.5 时显示出非常低的生产力，而 pH 值为 7.0 和 7.5 时则导致显著更高的比生产力和更高的浓度。将 pH 值从 7.0 增加到 7.5 并没有显示出显著的改善。然后，应该选择 pH 值为 7.0，因为它涉及到添加碱的成本较低。
