Continuous butanol production with reduced byproducts formation from glycerol by a hyper producing mutant of Clostridium pasteurianum

Abstract

Butanol, a four-carbon primary alcohol (C₄H₁₀O), is an important industrial chemical and has a good potential to be used as a superior biofuel. Bio-based production of butanol from renewable feedstock is a promising and sustainable alternative to substitute petroleum-based fuels. Here, we report the development of a process for butanol production from glycerol, which is abundantly available as a byproduct of biodiesel production. First, a hyper butanol producing strain of Clostridium pasteurianum was isolated by chemical mutagenesis. The best mutant strain, C. pasteurianum MBEL_GLY2, was able to produce 10.8 g l⁻¹ butanol from 80 g l⁻¹ glycerol as compared to 7.6 g l⁻¹ butanol produced by the parent strain. Next, the process parameters were optimized to maximize butanol production from glycerol. Under the optimized batch condition, the butanol concentration, yield, and productivity of 17.8 g l⁻¹, 0.30 g g⁻¹, and 0.43 g l⁻¹ h⁻¹ could be achieved. Finally, continuous fermentation of C. pasteurianum MBEL_GLY2 with cell recycling was carried out using glycerol as a major carbon source at several different dilution rates. The continuous fermentation was run for 710 h without strain degeneration. The acetone–butanol–ethanol productivity and the butanol productivity of 8.3 and 7.8 g l⁻¹ h⁻¹, respectively, could be achieved at the dilution rate of 0.9 h⁻¹. This study reports continuous production of butanol with reduced byproducts formation from glycerol using C. pasteurianum, and thus could help design a bioprocess for the improved production of butanol.