GASCHEM: Optimising industrial gas fermentation for commercial low-carbon fuel & chemical production through systems and synthetic biology approaches

预计到2030年，全球能源需求将增长40%。全球社会面临的主要挑战不仅是增加能源供应来源，而且还要最大限度地利用可持续形式的能源来保护环境，同时确保后者不会对粮食供应产生有害影响。在这方面，可再生能源将在全球一次能源供应中发挥越来越大的作用。英国政府，沿着大多数文明世界，现在已经为减少温室气体（GHG）设定了具有挑战性的目标。中心阶段是需要可持续地生产用于能源、润滑油和高价值化学品的碳氢化合物。通过生物系统生产化学品的传统途径一直依赖于将植物生物质中较易处理的成分（糖和淀粉）转化为化学品，特别是生物燃料。所使用的微生物发酵植物中容易获得的糖和/或淀粉，如甘蔗或玉米，并将其转化为生物燃料，最常见的是乙醇。这导致了人们对这些产品作为食物的竞争的担忧，并重新关注所谓的“第二代”生物燃料。它们分别由源自非粮食作物或农业废物的细胞壁材料（木质纤维素）产生，例如杨柳和稻草。细胞壁材料是光合作用的产物，植物将大气中的二氧化碳气体（CO2）转化为糖，然后用于组装复杂的碳基聚合物木质纤维素。对于微生物在植物细胞壁上的发酵生长，木质纤维素必须首先转化回单糖。然而，木质纤维素极耐分解。以具有成本效益的方式克服这种不确定性被证明是极具挑战性的。另一种途径是直接捕获碳，通过利用某些细菌的能力，典型的是Clostridium ljungdahli，“吃”气体一氧化碳（CO）。当将CO注入发酵容器的液体培养基中时，其被扬氏梭菌消耗并转化为乙醇。幸运的是，一氧化碳是一种丰富的资源，也是钢铁制造、炼油和化工生产等行业的废物。此外，它可以很容易地以合成气（“合成气”）的形式产生，通过气化（加热）林业和农业残留物，城市垃圾和煤。通过允许使用所有这些可用的低成本、非食物资源，这种方法既克服了与传统乙醇生产相关的“食物与燃料”问题，又规避了与“第二代”生物燃料相关的许多挑战。此外，捕获工业排放的大量CO（一旦释放到大气中就注定成为CO2）用于燃料和化学品生产，提供了化石碳排放的净减少。该项目的工业合作伙伴LanzaTech开发了一种基于这种“食气”细菌的多功能和强大的工艺，并证明了其从钢铁厂废气中生产化学品的能力。目前的产品包括乙醇和另一种醇（丁二醇），与乙醇不同，丁二醇具有作为有价值的化学品、溶剂或聚合物的潜力。诺丁汉大学开发了世界领先的遗传工具，可用于提高当前工艺的生产率，并扩大生物体可以生产的产品数量。通过共同努力，诺丁汉的工具将被用来提高我们对LanzaTech的“食气”昆虫如何将一氧化碳转化为化学物质的理解。此后，这些知识将被利用来增加现有产品的产量，并扩大可以制造的有用化学品的范围。

Global Energy demand is expected to increase by up to 40% by 2030. The key challenge facing the global community is to not only increase the sources of energy supply, but to also maximize the use of sustainable forms of energy to safeguard the environment while ensuring that the latter do not detrimentally impact food supplies. In this regard, renewable sources of energy will play an increasing role in the global primary energy supply. The UK government, along with the majority of the civilised world, have now set challenging targets for reductions in greenhouse gas (GHG). Centre stage is the need for the sustainable production of hydrocarbons for energy, lubricants, and high value chemicals. Traditional routes to chemical generation through biological systems have been reliant on the conversion of the more tractable components of plant biomass (sugars and starch) into chemicals, and in particular biofuels. The microbes employed ferment the easily accessible sugar and/or starch of plants, such as sugar cane or corn, and convert them into biofuels, most commonly ethanol. This has led to concerns over competition with use of these products as food, and a re-focussing of efforts on so-called 'second generation' biofuels. These are generated from cell wall material (lignocellulose) derived from non-food crops or agricultural wastes, such as willow and straw, respectively. Cell wall material is a product of photosynthesis, whereby plants convert atmospheric carbon dioxide gas (CO2) into sugars which are then used to assemble the complex carbon-based polymer, lignocellulose. For the fermentative growth of microbes on plant cell walls, lignocellulose must first be converted back into simple sugars. However, lignocellulose is extremely resistant to breakdown. Overcoming this recalcitrance in a cost effective manner is proving extremely challenging. An alternative route would be to directly capture carbon, by harnessing the ability of certain bacteria, typified by Clostridium ljungdahli, to 'eat' the gas carbon monoxide (CO). When CO is injected into the liquid medium of fermentation vessels it is consumed by Clostridium ljungdahlii and converted into ethanol. Fortunately, CO is an abundant resource, and a waste product of industries such as steel manufacturing, oil refining and chemical production. Moreover, it can be readily generated in the form of Synthesis Gas ('Syngas'), by the gasification (heating) of forestry and agricultural residues, municipal waste and coal. By allowing the use of all these available low cost, non-food resources, such a process both overcomes the "Food versus Fuel" issues associated with traditional ethanol production, and circumvents many of the challenges associated with 'second generation' biofuels. Furthermore, capturing the large volume of CO (destined to become CO2 once released into the atmosphere) emitted by industry for fuel and chemical production provides a net reduction in fossil carbon emissions. The Industrial Partner in this project, LanzaTech, have developed a versatile and robust process based on such a 'gas-eating' bacterium, and demonstrated its ability to produce chemicals from the off-gas of a Steel plant. Current products include ethanol, and another alcohol (butanediol) which, unlike ethanol, has potential as a valuable chemical, solvent or polymer. The University of Nottingham has developed world-leading genetic tools which can be used to both enhance the productivity of the current process, and extend the number of products the organism can make. Working together, the Nottingham tools will be used to improve our understanding of how LanzaTech's 'gas-eating' bugs convert carbon monoxide into chemicals. Thereafter, this knowledge will be exploited to both increase the yields of existing products, and extend the range of useful chemicals that can be made.