Engineering biobutanol production in a cellulosic clostridium using synthetic biology principles

目前，我们用来提供电力或运行汽车和其他车辆的燃料来自煤炭，石油和天然气。然而，这些“化石燃料”的可用性是有限的，并且预计到世纪中期，现有的资源将被耗尽。此外，现在显而易见的是，使用化石燃料产生二氧化碳，是造成全球变暖的一个主要因素。因此，对于使用更环保和可再生的系统来生产用于汽车和其它车辆的液体燃料（现在广泛地称为“生物燃料”）存在相当大的兴趣。因此，已经广泛采用在类似于酿造中使用的发酵过程中使用酵母从植物来源的淀粉生产乙醇。对这一进程进行两项根本性的改进将是有益的。一方面，可以生产更有效的燃料乙醇。另一方面，淀粉是人类饮食的重要组成部分，随着世界人口的增加和农业用地因全球变暖而减少，将不可能维持这种多糖用于人类消费和生物燃料生产之间的竞争。上述两种改进将通过开发用于大规模生产上级生物燃料丁醇的方法和通过开发能够将植物细胞衍生的木质纤维素转化为生物燃料的微生物来实现。丁醇的能量含量比乙醇高，可以利用现有的汽油供应和分销渠道，可以在比乙醇浓度更高的浓度下与汽油混合而无需对发动机进行改造，比汽油-乙醇混合物具有更好的燃料经济性，并且与乙醇不同，丁醇有可能用作航空燃料。木质纤维素是地球上最丰富的有机碳来源，既可再生，又不代表人类的食物来源。产生丁醇的细菌被称为“产溶剂的”，属于梭菌属，以丙酮丁醇梭菌为代表。虽然那些能产生丁醇的产溶剂菌种不能有效地降解木质纤维素，但有梭菌菌种的例子，如热纤梭菌，可以。这是一种称为“纤维素体”的特殊酶复合物的产生的结果，纤维素体是已知最有效的植物细胞壁降解系统之一。然而，产生纤维素体的细菌不产生丁醇，只产生乙醇。利用诺丁汉开发的专有专利技术，并借鉴目前BBSRC项目中有关C.我们将编码丁醇途径的基因导入C.利用合成生物学原理合成热纤素。将评估工程菌降解植物细胞壁和将产生的糖发酵成丁醇的能力。最终结果将是为第二代生物燃料生产创造更环保、更可持续的工艺。

Currently the fuels we use to provide electricity or to run cars and other vehicles is derived from coal, oil and gas. The availability of these 'fossil fuels,' however, is limited and it is projected that current sources will be exhausted by the middle of the 21st century. Furthermore, it is now apparent that the use of fossil fuels is a major contributor to global warming through the production of carbon dioxide. Thus, there is considerable interest into using more environmentally friendly and renewable systems for producing liquid fuels, now widely referred to as 'biofuels,' for cars and other vehicles. As a consequence there has been widespread adoption of the production of ethanol from plant derived starch using yeast in a fermentation process akin to that used in brewing. Two fundamental improvements to the process would be of benefit. On the one hand, more effective fuels to ethanol could be produced. On the other hand, starch is an important component of the human diet, and as the world population expands and agricultural land diminishes through global warming, it will be impossible to sustain the competition between the use of this polysaccharide for human consumption and biofuel production. The above two improvements would be met by developing a process for the large scale production of the superior biofuel, butanol, and by developing microbes able to convert plant cell derived lignocellulose into biofuel. Butanol has a higher energy content than ethanol, can make use of existing petrol supply and distribution channels, can be blended with petrol at higher concentrations than ethanol without engine modification, offers better fuel economy than petrol-ethanol blends and has, unlike ethanol, potential to be used as aviation fuel. Lignocellulose, the most abundant source of organic carbon on the planet, is both renewable and does not represent a human food source. The bacteria that produce butanol are called 'solventogenic' and belong to a group called Clostridium, typified by Clostridium acetobutylicum. Although those solventogenic species that can produce butanol are unable to efficiently degrade lignocellulose, there are examples of clostridial species, such as Clostridium thermocellum, that can. This is a consequence of the production of a specialised complex of enzymes called the 'cellulosome', one of the most efficient plant cell wall degrading systems known. Cellulosome-producing bacteria do not, however, produce butanol, only ethanol. Using proprietary, patented technology developed at Nottingham, and drawing on knowledge gained from a current BBSRC project concerned with metabolic engineering of the butanol pathway in C. acetobutylicum, we will take the genes which encode the butanol pathway, and introduce them into C. thermocellum using synthetic biology principles. The ability of the engineered bacterium to degrade plant cell walls and ferment the sugars generated into butanol will be evaluated. The net result will be the creation of more environmentally friendly, sustainable processes for second generation biofuel production.