Cameron D C, Altaras N E, Hoffman M L, Shaw A J
Department of Chemical Engineering, University of Wisconsin-Madison 53706-1691, USA.
Biotechnol Prog. 1998 Jan-Feb;14(1):116-25. doi: 10.1021/bp9701325.
Microbial fermentation is an important technology for the conversion of renewable resources to chemicals. In this paper, we describe the application of metabolic engineering for the development of two new fermentation processes: the microbial conversion of sugars to 1,3-propanediol (1,3-PD) and 1,2-propanediol (1,2-PD). A variety of naturally occurring organisms ferment glycerol to 1,3-PD, but no natural organisms ferment sugars directly to 1,3-PD. We first describe the fed-batch fermentation of glycerol to 1,3-PD by Klebsiella pneumoniae. We then present various approaches for the conversion of sugars to 1,3-PD, including mixed-culture fermentation, cofermentation of glycerol and glucose, and metabolic engineering of a "sugars to 1,3-PD" pathway in a single organism. Initial results are reported for the expression of genes from the K. pneumoniae 1,3-PD pathway in Saccharomyces cerevisiae. The best naturally occurring organism for the fermentation of sugars to 1,2-PD is Thermoanaerobacterium thermosaccharolyticum. We describe the fermentation of several different sugars to 1,2-PD by this organism in batch and continuous culture. We report that Escherichia coli strains engineered to express either aldose reductase or glycerol dehydrogenase convert glucose to (R)-1,2-PD. We then analyze the ultimate potential of fermentation processes for the production of propanediols. Linear optimization studies indicate that, under aerobic conditions, propanediol yields that approach the theoretical maximum are possible and CO2 is the primary coproduct. Without the need to produce acetate, final product titers in the range of 100 g/L should be possible; the high titers and low coproduct levels should make product recovery and purification straightforward. The examples given in this paper illustrate the importance of metabolic engineering for fermentation process development in general.
微生物发酵是将可再生资源转化为化学品的一项重要技术。在本文中，我们描述了代谢工程在开发两种新型发酵工艺中的应用：将糖类微生物转化为1,3 - 丙二醇（1,3 - PD）和1,2 - 丙二醇（1,2 - PD）。多种天然存在的生物体可将甘油发酵为1,3 - PD，但没有天然生物体能直接将糖类发酵为1,3 - PD。我们首先描述了肺炎克雷伯菌将甘油补料分批发酵为1,3 - PD的过程。然后介绍了将糖类转化为1,3 - PD的各种方法，包括混合培养发酵、甘油与葡萄糖的共发酵以及在单一生物体中构建“糖类到1,3 - PD”途径的代谢工程。报道了肺炎克雷伯菌1,3 - PD途径基因在酿酒酵母中的表达初步结果。将糖类发酵为1,2 - PD的最佳天然存在生物体是嗜热栖热放线菌属嗜热糖解菌。我们描述了该生物体在分批和连续培养中将几种不同糖类发酵为1,2 - PD的情况。我们报道了经工程改造表达醛糖还原酶或甘油脱氢酶的大肠杆菌菌株将葡萄糖转化为（R）- 1,2 - PD的情况。然后我们分析了丙二醇生产发酵工艺的最终潜力。线性优化研究表明，在有氧条件下，丙二醇产量有可能接近理论最大值，且二氧化碳是主要副产物。无需生产乙酸盐的情况下，最终产物滴度应能达到100 g/L；高滴度和低副产物水平应使产物回收和纯化变得简单。本文给出的例子总体上说明了代谢工程对发酵工艺开发的重要性。
