Takahashi C M, Takahashi D F, Carvalhal M L, Alterthum F
Departamento de Microbiologia, Universidade de São Paulo, Brazil.
Appl Biochem Biotechnol. 1999 Sep;81(3):193-203. doi: 10.1385/abab:81:3:193.
Escherichia coli KO11, in which the genes pdc (pyruvate decarboxylase) and adh (alcohol dehydrogenase) encoding the ethanol pathway from Zymomonas mobilis were inserted into the chromosome, has been shown to metabolize all major sugars that are constituents of hemicellulosic hydrolysates to ethanol, in anaerobic conditions. However, the growth and fermentation performance of this recombinant bacteria may be affected by acetic acid, a potential inhibitor present in hemicellulose hydrolysates in a range of 2.0-15.0 g/L. It was observed that acetate affected the growth of E. coli KO11, prolonging the lag phase and inducing loss of biomass production and reduction of growth rate. At lower pH levels, the sensitivity to acetic acid was enhanced owing to the increased concentration of the protonated species. On the other hand, the recombinant bacteria showed a high tolerance to acetic acid regarding fermentative performance. In Luria broth medium with glucose or xylose as a single sugar source, it was observed that neither yield nor productivity was affected by the addition of acetate in a range of 2.0-12.0 g/L, suggesting some uncoupling of the growth vs ethanol production.
大肠杆菌KO11已被证明在厌氧条件下能将半纤维素水解产物中的所有主要糖类代谢为乙醇，在该菌株中，来自运动发酵单胞菌的编码乙醇途径的基因pdc（丙酮酸脱羧酶）和adh（乙醇脱氢酶）被插入到染色体中。然而，这种重组细菌的生长和发酵性能可能会受到乙酸的影响，乙酸是半纤维素水解产物中存在的一种潜在抑制剂，浓度范围为2.0-15.0 g/L。据观察，乙酸会影响大肠杆菌KO11的生长，延长延迟期，并导致生物量产量损失和生长速率降低。在较低的pH值水平下，由于质子化物种浓度的增加，对乙酸的敏感性增强。另一方面，就发酵性能而言，重组细菌对乙酸表现出较高的耐受性。在以葡萄糖或木糖作为单一糖源的Luria肉汤培养基中，观察到在2.0-12.0 g/L的乙酸添加范围内，产量和生产率均未受到影响，这表明生长与乙醇生产之间存在某种解偶联现象。
