Hexanoic Acid Production from Syngas and Glucose By a Newly Isolated Strain Clostridium Sp. JS66

Syngas including CO and CO₂ gases is emitted from steel industrial facilities, causing global warming. Recently, gas fermentation of acetogenic bacteria utilizing syngas as carbon sources has been studied to produce valuable chemicals. In this study, we report a newly isolated strain Clostridium sp. JS66 as a hexanoic acid producer from syngas and glucose with high carbon conversion yields. Clostridium sp. JS66 exhibited 99.9% 16s rRNA similarity with Clostridium carboxidivorans P7, a known hexanoic acid-producing acetogen. But, distinct phenotypic differences and DNA-DNA hybridization value of 33 % to C. carboxidivorans P7 suggested that it is classified as a novel strain. Fermentation parameters; such as yeast extract concentration, temperature, and initial pH were optimized for cell growth. Also, lower agitation speed enhanced the production of hexanoic acid from 0.20 g/L to 0.49 g/L. In heterotrophic fermentation supplemented with glucose, H₂ and CO₂ evolved during fermentation was slowly consumed after glucose consumption. When mixotrophic fermentation supplemented with glucose and syngas (CO 30%, H₂ 40%, CO₂ 30%) was conducted, a small amount of CO was consumed during 25 hours. Interestingly, the yield of hexanoic acid on the basis of glucose was 0.276 g/g glucose which was 1.31-fold higher than the yield in heterotrophic fermentation (0.210 g/g glucose) after 25 hours, implying the potential of mixotrophic fermentation in efficient hexanoic acid production.