Caproic acid production through fermentation with a thermotolerant Clostridium strain M1NH

Abstract

Thermotolerant caproic acid-producing bacteria were isolated from sewage sludge and evaluated for caproic acid production with various substrates. The ethanol-acetate was the most efficient substrate for enriched culture, with 2.7 g/L caproic acid and a yield of 47%. Clostridium strain M1NH was isolated from enriched culture and identified as a gram-positive, rod-shaped, spore-forming with 92% similarity of 16S rRNA to Clostridium kluyveri. Clostridium M1NH has an optimal pH and temperature of 6-6.5 and 35–40°C with a growth rate of 0.11–0.14 h-1, suggesting that the strain was thermotolerant. Clostridium strain M1NH displays the highest caproic acid production of 3.2–3.5 g/L at a pH of 6.5, a temperature of 35–40°C, and an ethanol-acetate molarity ratio of 4:1. Clostridium strain M1NH is tolerant to concentrations of ethanol, acetate, and caproic acid of 5%, 5%, and 2%, respectively. The thermotolerant Clostridium M1NH presents a significant advancement in harnessing sustainable biobased production processes, holding great promise for applications in thermotolerant fermentation.