Engineering biobutanol production in a cellulosic clostridium using synthetic biology principles

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.