Butanol production by Clostridium

Abstract

Abstract Clostridium are Gram-positive, strictly anaerobic, endospore-forming bacteria that can produce a variety of chemicals including n-butanol. Traditional bio-based n-butanol is produced via ABE (acetone–butanol–ethanol) fermentation by Clostridium, which cannot compete with petrochemical-based butanol for price, mainly due to low fermentation yield and titer. Recombinant Clostridium can also be used as hosts for isobutanol production. This chapter reviews advances in metabolic engineering and process engineering for improved butanol production by Clostridium. A number of genetic manipulation tools have been developed for solventogenic Clostridium such as C. acetobutylicum, but for most strains of Clostridium, plasmid transformation and gene manipulation still remain a problem. Metabolic engineering to construct strains with enhanced butanol yield, titer, productivity, and improved industrial performances has been performed. Process engineering such as high-cell-density fermentation for high butanol productivity and in situ butanol recovery to alleviate butanol toxicity has been applied to various Clostridium strains. The excellent substrate diversity of Clostridium allows its conversion of inexpensive substrates to butanol. Metabolic and process engineering for enhanced utilization of lignocellulose, syngas, and glycerol has made significant achievements but still not enough for economical biobutanol production from these inexpensive substrates. Green Biologics is currently the main industrial biobutanol producer in the United States. Future efforts are expected to combine desirable phenotypes, such as hyper-butanol production, high butanol tolerance, and excellent lignocellulose utilization ability. A deeper understanding of the basic mechanisms of cell metabolism for butanol production, butanol tolerance, sporulation, etc. is also crucial.