Genetics of Butanol‐producing Strains

n -Butanol is a four-carbon alcohol that contains one hydroxyl group at carbon position one. Butanol is currently commercially synthesized by hydroformylation of propylene gas with hydrogen and carbon monoxide gases. The reaction of propylene and carbon monoxide initially results in the formation of n -butyraldehyde, which is further hydrogenated to n-butanol. Butanol is also produced through a fermentative process termed acetone–butanol–ethanol (ABE) fermentation, in which solventogenic Clostridium species anaerobically transform renewable raw resources, such as sugars derived from starch or lignocellulosic biomass, and other substrates into butanol and other solvents. The chemical synthesis of butanol from propylene (fossil gas) is called the oxo process, which is more cost-efficient than ABE fermentation. Biobutanol is a promising fuel with a higher energy density, lower hygroscopicity and better engine compatibility than ethanol. In addition to its use as a biofuel, biobutanol has industrial uses as a solvent for the manufacture of a wide range of products, including paints, plastics, adhesives, coatings, and polymers. However, the butanol fermentation process presents considerable production challenges, despite its potential to replace fossil fuels. Solventogenic Clostridium species, particularly Clostridium beijerinckii and Clostridium acetobutylicum , are the primary microbial workhorses for ABE fermentation, yet their industrial application is constrained by butanol toxicity, low titers (∼9–14 g/L in batch processes), and metabolic inefficiencies. Understanding the molecular basis of butanol toxicity and production can uncover key genes and pathways for engineering Clostridium species with improved tolerance and product yield. This chapter delves into genomic analyses of solventogenic Clostridium species, uncovering significant diversity of species ranging from genome size to carbohydrate metabolism, membrane synthesis, and heat shock genes. It also details potential mechanisms regulating butanol production and toxicity. Additionally, this chapter elaborates on strategies for feasible large-scale biobutanol production that could support global renewable energy initiatives and environmental sustainability.