The potential of caproate (hexanoate) production using syntrophic cocultures with or .

Caproate (hexanoate) and other medium-chain fatty acids are valuable platform chemicals produced by processes utilizing petroleum or plant oil. , growing on short chain alcohols (notably ethanol) and carboxylic acids (such as acetate) is noted for its ability to perform chain elongation to produce 4- to 8-carbon carboxylates. has been studied in monoculture and coculture conditions, which lead to relatively modest carboxylate titers after long fermentation times. To assess the biosynthetic potential of for caproate production from sugars through coculture fermentations, in the absence of monoculture data in the literature suitable for our coculture experiments, we first explored monocultures. Some monocultures achieved caproate titers of 150 to over 200 mM in 40-50 h with a production rate of 7.9 mM/h. Based on that data, we then explored two novel, syntrophic coculture partners for producing caproate from sugars: and . Neither species has been cocultured with before, and both demonstrate promising results. Our experiments of monocultures and - cocultures demonstrate exceptionally high caproate titers (145-200 mM), fast production rates (3.25-8.1 mM/h), and short fermentation times (18-45 h). These results represent the most caproate produced by a coculture in the shortest known fermentation time. We also explored the possibility of heterologous cell fusion between the coculture pairs similar to the results seen previously in our group with and Fusion events were observed only in the - coculture pair, and we offer an explanation for the lack of fusion between and . This work supports the promise of coculture biotechnology for sustainable production of caproate and other platform chemicals.