Genetic modification of critical enzymes and involved genes in butanol biosynthesis from biomass

Interest in biobutanol, a sustainable vehicle fuel, is increasing due to rising oil prices and concerns of surrounding climate change and the energy crisis. However, the costs of biobutanol with conventional ABE fermentation by Clostridium are higher than the cost of butanol from today's petrochemical processes. Two major problems in the economic production of biobutanol are difficulty controlling the induction of a metabolic shift from acidogenesis to solventogenesis and limitations imposed by severe product inhibition. With developments in biotechnology, and the completion of genome sequencing of Clostridium, genetic modification is a viable method to improve the solvent yield and the butanol production ratio. The present article aims to highlight the latest research progress on overexpressing, inserting, knocking out, and knocking down genes of the key enzymes in the ABE fermentation pathway and other relative genes (such as genes coding for heat-shock proteins, operon, transcription, etc). Recombinant manipulations of these genes in Escherichiacoli and yeast have also been reported recently, although their butanol yields are lower than in Clostridium. Butanol production with solventogenic clostridia from various feedstocks is also evaluated in this review.