Regulation on C2-C8 carboxylic acid biosynthesis from anaerobic CO2 fermentation

Abstract

Bioconversion of CO2 into liquid fuels or chemicals, preferred medium chain carboxylic acids (caproic and caprylic acid), is an attractive CO2 utilization technology. The present study aims to investigate the effects of different ratios of H2/CO2 on regulating the distribution of C2-C8 carboxylic acid products, while the headspace pressure of 1.5 bar was set to amplify the effect of different ratios. The H2/CO2 ratio of 4:1 was more suitable for preparing acetic acid, where the highest acetic acid yield was 17.5 g/L. And the H2/CO2 ratio of 2:1 showed excellent chain elongation ability with the highest n-caprylic yield of 2.4 g/L. Additionally, the actual H2/CO2 ratios of 4:1 reactors were higher than that in 2:1 may be course chain elongation often accompanied by H2 production. The 16S rRNA genes analysis shows that the genus Terrisporobacter and Coriobacteriales may be related to acetic acid production enriched in H2/CO2 ratio 4:1 reactors, and the genus Clostridium and Paenibacillaceae may associate with the chain elongation pathway were enriched in H2/CO2 ratio 2:1 reactors.