Chain Elongation by Clostridium kluyveri: Effect of Substrates

The microbial conversion of C1 gas produced by the gasification of C-based streams (e.g., biomass and plastic) is a promising strategy for the production of bioalcohols and biocommodities. Acetogenic bacteria can produce value-added metabolites, such as acetate and butyrate, but their recovery is costly and energy intensive. The success of exploiting these acids may be their conversion into medium-chain fatty acids (MCFAs), such as n-caproic and n-caprylic acids, in a second fermentation step. Interest in MCFAs is related to their high hydrophobicity, high values, and high energy densities. These MCAF features make them better suited for chemical manufacturing and as biofuel precursors. Clostridium kluyveri is known for its ability to produce MCFAs under anaerobic fermentation via the reverse β-oxidation pathway. The present study reports the recent results of the characterization of C. kluyveri fermentation under batch conditions. In particular, attention was paid to assessing the effects of substrate composition on the production of MCFAs. Experiments were carried out in 0.25 L MiniBio bioreactors (Applikon), working volume of 0.12 L, operated at 37 °C and Ph = 6.8. The investigated substrates were acetic acid, ethanol, and butyric acid. The conversion process was characterized in terms of substrate conversion, metabolite and cell production, specific rates of cells/metabolite production, and yields. The results indicated that C. kluyveri preferred acetic acid and ethanol as carbon sources for growth. Supplementation of butyric acid in the fermentation medium was associated with a high production of hexanoic acid.