Ethanol production from xylose with a pyruvate-formate-lyase mutant of Klebsiella planticola carrying a pyruvate-decarboxylase gene from Zymomonas mobilis

The Role of the Pyruvate Acetyl-CoA Switch in the Production of 1,3-Propanediol by Klebsiella pneumoniae

Pyruvate dehydrogenase-complex (AcoABCD) and pyruvate formate-lyase (PFL) are two pathways responsible for synthesis of acetyl-CoA from pyruvate (pyruvate acetyl-CoA switch). The two pathways were individually deleted in Klebsiella pneumoniae, and the role of the pyruvate acetyl-CoA switch in 1,3-propanediol production was investigated. Fermentation results showed that the two pathways were both active in the wild-type strain. Acetyl-CoA formation between the two pathways was equal in the wild-type strain. The pflB mutant produced high level of lactic acid, and deletion of ldhA eliminated lactic acid synthesis. The conversion ratio of glycerol to 1,3-propanediol in the pflB-ldhA mutant reached 0.541 g/g, which was 9.4 % higher than that of the wild-type strain. However, the productivity of 1,3-propanediol was decreased in the pflB-ldhA mutant. In contrast, the productivity of 1,3-propanediol was increased by 19 % in the acoABCD mutant, with the disadvantage of lower substrate conversion ratio. Regulating the pyruvate acetyl-CoA switch presents a novel way to improve the conversion ratio or productivity of 1,3-propanediol produced by K. pneumoniae.

Cellular and metabolic engineering. An overview

Metabolic engineering is defined as the purposeful modification of intermediary metabolism using recombinant DNA techniques. Cellular engineering, a more inclusive term, is defined as the purposeful modification of cell properties using the same techniques. Examples of cellular and metabolic engineering are divided into five categories: 1. Improved production of chemicals already produced by the host organism; 2. Extended substrate range for growth and product formation; 3. Addition of new catabolic activities for degradation of toxic chemicals; 4. Production of chemicals new to the host organism; and 5. Modification of cell properties. Over 100 examples of cellular and metabolic engineering are summarized. Several molecular biological, analytical chemistry, and mathematical and computational tools of relevance to cellular and metabolic engineering are reviewed. The importance of host selection and gene selection is emphasized. Finally, some future directions and emerging areas are presented.

Zymomonas mobilis--science and industrial application

Zymomonas mobilis is undoubtedly one of the most unique bacterium within the microbial world. Known since 1912 under the names Termobacterium mobilis, Pseudomonas linderi, and Zymomonas mobilis, reviews on its uniqueness have been published in 1977 and 1988. The bacterium Zymomonas mobilis not only exhibits an extraordinarily uniqueness in its biochemistry, but also in its growth behavior, energy production, and response to culture conditions, as well as cultivation techniques used. This uniqueness caused great interest in the scientific, biotechnological, and industrial worlds. Its ability to couple and uncouple energy production in favor of product formation, to respond to physical and chemical environment manipulation, as well as its restricted product formation, makes it an ideal microorganism for microbial process development. This review explores the advances made since 1987, together with new developments in the pure scientific and applied commercial areas.

Metabolic engineering of Klebsiella oxytoca M5A1 for ethanol production from xylose and glucose

The efficient diversion of pyruvate from normal fermentative pathways to ethanol production in Klebsiella oxytoca M5A1 requires the expression of Zymomonas mobilis genes encoding both pyruvate decarboxylase and alcohol dehydrogenase. Final ethanol concentrations obtained with the best recombinant, strain M5A1 (pLOI555), were in excess of 40 g/liter with an efficiency of 0.48 g of ethanol (xylose) and 0.50 g of ethanol (glucose) per g of sugar, as compared with a theoretical maximum of 0.51 g of ethanol per g of sugar. The maximal volumetric productivity per hour for both sugars was 2.0 g/liter. This volumetric productivity with xylose is almost twice that previously obtained with ethanologenic Escherichia coli. Succinate was also produced as a minor product during fermentation.

Effects of environmental conditions on xylose fermentation by recombinant Escherichia coli

In batch fermentations, optimal conversion of xylose to ethanol by recombinant Escherichia coli was obtained under the following conditions: 30 to 37 degrees C, pH 6.4 to 6.8, 0.1 to 0.2 M potassium phosphate buffer, and xylose concentrations of 8% or less. A yield of 39.2 g of ethanol per liter (4.9% ethanol by volume) was observed with 80 g of xylose per liter, equivalent to 96% of the maximum theoretical yield. Maximal volumetric productivity was 0.7 g of ethanol per liter per h in batch fermentations and 30 g of ethanol per liter per h in concentrated cell suspensions (analogous to cell recycling).