(228af) Production of n-Butanol and Ethanol from Biodiesel-Glycerol By Engineered Clostridium Formicoaceticum

With concerns about the high oil price and greenhouse gas emissions, biofuels have gained large attention from industry and government. Nowadays, more and more research has focused on the development of sustainable bioprocesses for bio-butanol production. n-Butanol, a four-carbon primary alcohol (C₄H₁₀O), is a significant industrial chemical and has a great potential to be used as a superior biofuel. Especially, compared with ethanol, n-butanol can be used as an ideal substitute of gasoline because of its low water solubility, high energy density, and low vapor pressure. Unfortunately, bio-butanol production using the conventional acetone-butanol-ethanol (ABE) fermentation process is not economically feasible because of the co-production of other metabolites, including CO₂, acetone, acetate, and butyrate, resulting in a low butanol yield. In this study, we focuses on a homoacetogen, Clostridium formicoaceticum, which naturally produces acetic acid as the sole fermentation product from a carbon source, such as fructose, lactate and glycerol, with a high product yield of >90% (w/w) without losing any carbon to CO₂. Based on the analysis of recently sequenced whole genome, C. formicoaceticum has all the genes needed for glycerol utilization and Wood-Ljungdahl pathways, suggesting that C. formicoaceticum can utilize glycerol and CO₂ as carbon sources to produce acetate. In this study, we introduced thl, hbd, crt, bcd-etfB-etfA, and adhE2 genes from Clostridium acetobutylicum into C. formicoaceticum and investigated ethanol and n-butanol production from crude glycerol present in biodiesel wastewater by the engineered mutant. The result showed that C. formicoaceticum is a promising heterologous host for biofuel production from cheap and abundant industrial byproducts and its use can further reduce CO₂ emission.