(614a) Conversion of CO2 into C2-C6 Products By Clostridium Muellerianum Sp. Nov. Strain P21

Global CO₂ emissions have reached over 36 billion tons. Capturing and direct conversion of CO₂ into various products via a robust technology makes economic sense and can reduce greenhouse gas (GHG) emissions. Electrochemical, photochemical and thermochemical methods have been used to recycle CO₂ into products such as cement, methane, methanol and formic acid. However, these methods are energy intensive and suffer from low conversion efficiency and catalysts poisoning. Alternatively, biological methods can be used for the direct conversion of CO₂ into biofuels and other products at near ambient temperature and pressure, reducing GHG. In the present study the effects of medium components and inoculum preparation on the ability of a novel Clostridium muellerianum strain P21 to convert CO₂ into C₂ – C₆ alcohols and fatty acids were investigated. C. muellerianum is an acid/alcohol producing, Gram stain positive, rod-shaped acetogen. CO₂ fermentations were performed using nutrient limited and nutrient rich media. Nutrient limited medium contains only three vitamins (pantothenate, p-(4)-Aminobenzoic Acid, and Biotin). In addition to these vitamins, nutrient rich medium contains pyridoxine, thiamine, riboflavin, thioctic acid, nicotinic acid, vitamin B12, folic acid and mercaptoethanesulfonic acid sodium salt (MESNA). CO₂ fermentations were performed using strain P21 inocula prepared using syngas (CO:CO₂:H₂) and CO₂:H₂. CO₂ fermentations were performed in 250 mL bottle assays with 50 mL working volume at 37°C and 125 rpm. CO₂:H₂:N₂ (20:60:20) gas mix was fed daily for 360 h. Results showed that strain P21 converted CO₂ into C₂ – C₆ alcohols and fatty acids. In addition, strain P21 grew faster on CO₂ and produced 2.8- and 2.1-fold more alcohols and fatty acids, respectively, in nutrient rich medium compared to nutrient limited medium. Therefore, nutrient rich medium was used for further experiments. Strain P21 produced ethanol (1.9 g/L), acetic acid (3.6 g/L), butanol (0.8 g/L), butyric acid (0.8 g/L), hexanol (0.3 g/L) and hexanoic (0.3 g/L) from CO₂ in the assay bottles with the inoculum prepared with syngas. Strain P21 produced 2.0- and 4.2-fold more ethanol and butanol from CO₂ using the inoculum prepared with syngas as compared to CO₂:H₂ inoculum. Moreover, CO₂ and H₂ uptake rates by the new strain P21 were 33% and 17% higher with the syngas inoculum. Additional results on CO₂ fermentations in 3L-stirred tank reactor and other operating parameters will be presented. This research is expected to advance the biological conversion of CO₂ into valuable products with increased carbon utilization and economic feasibility.