Synthetic approaches towards the production of biofuels from lignocellulosic feedstocks in yeast

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The construction and integration of new pathways and systems into organisms for the production of useful metabolites is a key area of synthetic biology. The brewers' yeast (Saccharomyces cerevisiae) is a biotechnological workhorse; it has been used for the production of foods and beverages for centuries. More recently, this organism has been central to the production of the biofuel, bioethanol. Saccharomyces cerevisiae also serves as a model organism in molecular and cell biology, biochemistry and genetics. Studies on this yeast have pioneered the transition into the genomic and post-genomic era. For instance, S. cerevisiae was the first organism to have its genome sequenced and it has the most comprehensive compilation of gene expression data and systematic mutant collections. Probably as a result, much of the data, tools and technologies of systems biology have been developed in this yeast. This combination of a long, successful history of biotechnological application and unprecedented tools and resources make S. cerevisiae an ideal host for synthetic biology. We have introduced a pathway that allows the production of biobutanol in S. cerevisiae. Biobutanol is viewed as a superior biofuel to bioethanol; perhaps most fundamentally, as it can be used directly in vehicles without engine modification and it is non-corrosive allowing transportation via existing pipelines. The design strategies that we have employed in the integration of this pathway, have improved the yield about 100-fold relative to other published studies. However, there is further optimisation and development required before the strains would be applicable in an industrial context. Therefore, the first aim of this proposal is to optimise the production of biobutanol from this strain. We will assess the efficiency of the added enzymes, we will alter endogenous metabolism to channel metabolites towards the butanol production pathway and we will minimise the production of contaminants such as ethanol.A second goal is to extend the feedstock range such that our butanol producing strain can make maximal use of the resources available in lignocellulosic-based feedstocks. For example, wheat fed bioethanol refineries, like those in the UK, use only the starch rich endosperm (within the seed). Our proposed strain could potentially use a much greater proportion of the plant as a feedstock. A final overarching goal running through the proposal is to develop mathematical models that accurately recapitulate levels of butanol production in various mutants under a variety of conditions. The model can then be used to predict genetic alterations that would lead to further enhancements of butanol yield. The impact of these predictions on butanol yield would ultimately be assessed.Overall, the project aims to generate yeast strains with the capacity to produce an environmentally clean biofuel from renewable energy sources.