Modification of yeast for the production of butanol by metabolic engineering

n-butanol represents a key building block chemical in the solvent industry and holds significant promise as a biofuel. We have used metabolic engineering to develop novel yeast strains that can produce n-butanol. We have assembled a genomic integration system to allow expression of a series of heterologous genes from the ABE pathway of Clostridia in butanol-resistant yeast strains. To channel carbon flow into this butanol pathway and moderate any redox imbalance, the major alcohol dehydrogenase gene ADH1 was deleted. Key extracellular metabolite changes in this butanol production strain were surveyed by GCMS in batch experiments. Accumulation of acetaldehyde, 2-butenal and 2,3-butanediol suggest competing pathways are operating. Further engineering to overcome these issues has successfully generated yeast strains that produce higher levels of butanol. The efficiency of variant ABE pathways was evaluated to establish the contribution of each enzyme to n-butanol biosynthesis. This work represents an excellent starting point for further refinement and adaptation of butanol production in S. cerevisiae towards more commercially competitive yields.