Coproduction of 1,3-propanediol and 3-hydroxypropionic acid from glycerol by Clostridium pasteurianum

主要由化石燃料燃烧引起的人为二氧化碳排放正在导致大气中二氧化碳浓度的增加。日益加剧的环境担忧和气候变化方面的不确定性以及这些燃料不可避免的局限性，要求开发替代的、可持续的燃料和化学品生产途径。生物替代品的开发主要集中在糖基发酵上。然而，这些加工过程受到可食用原料成本的影响。另一种价格较低的原料是生甘油，这是生产生物柴油的主要副产品。生物柴油经济的增长导致这种原料的价格大幅下降。这种副产品的处理对生物柴油公司来说是一个沉重的负担。甘油的利用将提高从原料中回收有价值的产品，并通过降低产品价格而有利于生物柴油的生产。甘油利用的一个有希望的候选者是严格厌氧细菌巴氏梭菌。梭状芽孢杆菌属细菌在底物的灵活性和对有毒化合物的耐受性方面比经典的模式生物如酿酒酵母或大肠杆菌具有巨大的优势。然而，用于研究和改造这些生物体的复杂的遗传工具才刚刚开始出现。巴氏杆菌天然地从甘油1，3-丙二醇(1，3-PD)中产生最终产物，甘油1，3-丙二醇是一种工业上有价值的化学中间体，可用于合成聚合物，如聚酯。当甘油生成1，3-PD以提供必要的还原当量时，代谢限制会不可避免地导致副产物的形成。将这些天然的低价值副产品转变为更理想的产品，如3-羟丙酸(3-HP)，可以大幅降低产品的价格。3-HP是合成商品和特种化学品的一种很有前途的C3构筑块，可还原为1，3-PD。拟议的项目旨在对巴氏杆菌进行代谢工程，以从甘油中联产1，3-PD和3-HP。因此，将引入一条通向3-HP的异源途径，并培育天然的1，3-PD途径。此外，基因改造将防止不想要的副产品的形成。这一可持续的过程将使用廉价和丰富的甘油原料，并产生重要的化学成分，有望有助于改善和支持生物柴油的生产。该项目不仅将为生产有价值的化学品带来令人满意的生物转化，而且有望导致迄今不发达的用于工业和医学上重要的梭状芽胞杆菌属细菌的遗传工具的改进和进步。这也将提高对新陈代谢的理解。

Human-caused CO2 emissions predominantly caused by the combustion of fossil fuels is leading to increased atmospheric CO2 concentrations. Rising environmental concerns and uncertainties regarding the climate changes and the inevitable limitation of these fuels necessitate the development of alternative, sustainable routes to fuels and chemical production. Developments of biological alternatives have been mainly focused on sugar-based fermentations. However, these processes suffer from the cost of the edible feedstock. One alternative less expensive feedstock is raw glycerol, the primary by-product of biodiesel production. Growth of the biodiesel economy led to a significant decrease of the price of this feedstock. Disposal of this by-product is a severe burden for biodiesel companies. Utilization of glycerol would improve the recovery of valuable products from the feedstock and benefit biodiesel production by lowering the price of the product. One promising candidate for glycerol utilization is the strictly anaerobic bacterium Clostridium pasteurianum. Bacteria of the genus Clostridium have tremendous advantages over classic model organisms such as Saccharomyces cerevisiae or Escherichia coli with respect to flexibility of substrates utilized and tolerance to toxic compounds. However, sophisticated genetic tools for study and modification of these organisms have just started to become available. C. pasteurianum naturally produces as end-product from glycerol 1,3-propanediol (1,3-PD), an industrially valuable chemical intermediate that can be used, for example, for the synthesis of polymers such as polyesters. Metabolic constraints lead to inevitable by-product formation when 1,3-PD is produced from glycerol to provide necessary reducing equivalents. Changing these natural low value by-products to a more desirable such as 3-hydroypropionic acid (3-HP) can drastically lower the price of the product. 3-HP is a promising C3 building block for the synthesis of commodity as well as specialty chemicals and can be reduced to 1,3-PD. The proposed project aims at the metabolic engineering of C. pasteurianum for the coproduction of 1,3-PD and 3-HP from glycerol. Therefore, a heterologous pathway leading to 3-HP will be introduced and the native pathway to 1,3-PD will be fostered. Furthermore, genetic modifications will prevent the formation of unwanted side products. This sustainable process will employ the cheap and abundant feedstock glycerol and generate important chemical building blocks and will hopefully help to improve and support biodiesel production. The project will not only lead to a desirable biological conversion for the production of valuable chemicals but will hopefully lead to improvements and advances of the so far underdeveloped genetic tools for bacteria of the industrially and medically important genus Clostridium. It will also improve the understanding of the metabolism.