School of Biotechnology, Jiangnan University, Wuxi 214122, PR China.
Metab Eng. 2010 Sep;12(5):420-8. doi: 10.1016/j.ymben.2010.06.001. Epub 2010 Jun 12.
Ethanologenic Thermoanaerobacter species produce ethanol from lignocellulose derived substrates at temperatures above 70 degrees C. In the final steps of ethanol formation, two bifunctional acetaldehyde/alcohol dehydrogenases, AdhB and AdhE, and an alcohol dehydrogenase, AdhA, catalyze redox reactions between acetyl-CoA and ethanol via an acetaldehyde intermediate. DNA cloning and analysis revealed that the dehydrogenase genes and their transcriptional regulatory regions were highly conserved in these species. As determined by real-time PCR, the transcription of adhE was activated by ethanol, while adhB was transcribed without ethanol; however, all of their transcription was reduced at higher ethanol concentrations. Under imitating physiological conditions, AdhE played a crucial role in ethanol formation, and AdhB favored ethanol consumption when ethanol concentration was high e.g. 1%. Thus, the ethanol titer of fermentation is controlled via transcriptional regulation and the properties of specific enzymes in Thermoanaerobacter. These results provide evidence for an ethanol balance model and offer the possibility to raise the ethanol titer by metabolic engineering.
产乙醇热厌氧杆菌属的物种能够在 70°C 以上的温度下，从木质纤维素衍生的基质中生产乙醇。在乙醇形成的最后步骤中，两种双功能乙醛/乙醇脱氢酶（AdhB 和 AdhE）和一种乙醇脱氢酶（AdhA）通过乙醛中间产物，催化乙酰辅酶 A 和乙醇之间的氧化还原反应。DNA 克隆和分析表明，这些物种中的脱氢酶基因及其转录调控区高度保守。实时 PCR 测定结果表明，adhE 的转录受乙醇激活，而 adhB 则在没有乙醇的情况下转录；然而，在较高的乙醇浓度下，它们的转录都减少了。在模拟生理条件下，AdhE 在乙醇形成中起着关键作用，而当乙醇浓度较高（例如 1%）时，AdhB 则有利于乙醇消耗。因此，发酵过程中乙醇的产量受到转录调控和热厌氧杆菌属特定酶的特性的控制。这些结果为乙醇平衡模型提供了证据，并为通过代谢工程提高乙醇产量提供了可能性。
