Microbial (electro-)elongation of acetate to medium chain carboxylates

When suitably fed with reducing equivalents, some microorganisms are able to fermentatively elongate short chain fatty acids (e.g. acetate) to medium chain fatty acids (MCFA, e.g. caproate) (Agler et al., 2010). MCFA are valuable platform chemicals with many applications in the field of food additives, biopesticides, solvents, fragrances, biofuels, ... The low water solubility of MCFA also makes their recovery relatively easy, as compared to acetate. In order to master the chain elongation process to convert biowaste to MCFA, our aim is to investigate the influence of the source of reducing equivalents on the elongation of acetate to MCFA. Natural microbial consortia fed with acetate were incubated with different source of reducing equivalents, ie a biocathode and hydrogen gas. The acetate consumption and MCFA production were monitored as a function of time under batch and fed batch conditions. Massbalance show that both reducing equivalents sources allow acetate consumption and up to caprylate production (C8).