Lawford H G, Rousseau J D
Department of Biochemistry, University of Toronto, Ontario, Canada.
Appl Biochem Biotechnol. 1996 Spring;57-58:277-92. doi: 10.1007/978-1-4612-0223-3_25.
The pet operon consists of genes coding for enzymes responsible for ethanol production and consists of pyruvate dehydrogenase and alcohol dehydrogenase II from the high-performance ethanologen Zymomonas mobilis. This article describes the physiological influence of pet expression in Escherichia coli B (ATCC 11303) in terms of growth rate and overall concentrations of cell mass and catabolic end products achieved under well-defined cultivation conditions that included constant pH and carbon (energy) limitation. Glucose, mannose, and xylose were used as substrates, because they represent the principal fermentable components of lignocellulosic biomass and because fermentation of these sugars involves different metabolic pathways. Two different types of ethanologenic recombinants were used-a strain in which pet expression was via a multicopy plasmid (pLO1297) and a chromosomal integrant, strain KO11. Under the condition of sugar substrate limitation, there was no growth enhancement by pet expression with either glucose or mannose. Whereas the host strain produced exclusively lactic acid from glucose and mannose, both recombinants produced mostly ethanol. Both the plasmid-carrying strain and the pet integrant exhibited slower growth compared to the host culture with glucose or mannose as fermentation substrate. With mannose, the plasmid recombinant grew appreciably slower than either the host culture or the recombinant KO11. Use of a magnesium-deficient medium produced different results with glucose since substrate and turbidometric measurements proved to be unreliable in terms of estimating overall biomass levels. At pH 6.3, pet expression improved overall biomass yield; but at pH 7.0, the cell yields exhibited by the plasmid recombinant and the host strain were the same. E. coli B did not grow well on xylose as sole carbon source. With xylose, pet expression increased the growth rate, but had no effect on the overall biomass yield. In comparing our observations with the reports of others, it was concluded that the effect of pet expression on growth of E.coli is dependent on several different biochemical, physiological, genetic, and environmental factors, which largely precludes a statement of generality regarding this phenomenon.
pet操纵子由编码负责乙醇生产的酶的基因组成，由来自高效产乙醇菌运动发酵单胞菌的丙酮酸脱氢酶和乙醇脱氢酶II组成。本文描述了在包括恒定pH值和碳（能量）限制的明确培养条件下，pet在大肠杆菌B（ATCC 11303）中的表达对生长速率以及细胞质量和分解代谢终产物总浓度的生理影响。使用葡萄糖、甘露糖和木糖作为底物，因为它们代表木质纤维素生物质的主要可发酵成分，并且因为这些糖的发酵涉及不同的代谢途径。使用了两种不同类型的产乙醇重组体——一种是通过多拷贝质粒（pLO1297）表达pet的菌株和一个染色体整合体KO11菌株。在糖底物限制的条件下，用葡萄糖或甘露糖时，pet表达并未促进生长。宿主菌株仅从葡萄糖和甘露糖产生乳酸，而两种重组体主要产生乙醇。与以葡萄糖或甘露糖作为发酵底物的宿主培养物相比，携带质粒的菌株和pet整合体的生长都较慢。对于甘露糖，质粒重组体的生长明显比宿主培养物或重组体KO11慢。使用缺镁培养基对葡萄糖产生了不同的结果，因为底物和比浊法测量在估计总生物量水平方面被证明是不可靠的。在pH 6.3时，pet表达提高了总生物量产量；但在pH 7.0时，质粒重组体和宿主菌株的细胞产量相同。大肠杆菌B在木糖作为唯一碳源时生长不佳。对于木糖，pet表达提高了生长速率，但对总生物量产量没有影响。在将我们的观察结果与其他人的报告进行比较时，得出的结论是，pet表达对大肠杆菌生长的影响取决于几个不同的生化、生理、遗传和环境因素，这在很大程度上排除了对这一现象进行一般性陈述的可能性。
