Engineering clostridia for butanol production from biorenewable resources: from cells to process integration

•Lignocellulosic biomass and CO2 are readily available and low cost but difficult to ferment.•Clostridia can utilize cellulose or CO2 to produce ethanol and acetic acid, but not butanol.•Metabolic engineering of cellulolytic and acetogenic Clostridium for butanol production is discussed.•Co-culturing these microbes in CBP could theoretically produce butanol from cellulose and CO2 economically.

Renewable feedstocks such as lignocellulosic biomass, CO2 and syngas are readily available and low cost but difficult to ferment. There are microbes that can utilize cellulose or gases to produce ethanol and organic acids as major products, but few can produce n-butanol in a significant amount. Metabolic engineering can be applied to both cellulolytic and acetogenic clostridia to produce n-butanol directly from cellulose and CO2. In addition, co-culturing these engineered microbes can utilize cellulose directly and CO2, produced via the fermentation, in an integrated process for butanol fermentation and recovery. This review focuses on the development of consolidated bioprocessing (CBP) using engineered clostridia for n-butanol production from biorenewable resources such as lignocellulosic biomass and CO2.