Key subcommunity dynamics of medium-chain carboxylate production in anaerobic fermentation reactors

Today the provision of platform chemicals and liquid fuels is still predominantly based on fossil resources and needs to be substituted by biomass conversions to facilitate a circular bioeconomy.A comparison of the readily available technologies for this task, such as thermochemical conversion, the sugar platform, and the carboxylate platform has shown the highest overall yields for the carboxylate platform (Holtzapple and Granda 2009).The next level which needs to be reached for the platform chemicals to be part of the real bio-economy is the use of monitored and engineered anaerobic fermentations. Indeed, short-chain fatty acids are naturally produced by the microbial population which is in the reactor during this fermentation process. Those short-chain fatty acids can be elongated to medium-chain fatty acids (MCFAs, mainly C5 – C8) (Kallscheuer et al. 2017) using the reversed ß-oxidation pathway (Agler et al. 2011; Spirito et al. 2014).In this study we followed over time the production of short- and medium-chain fatty acids (acetate, butyrate, caproate and caprylate) impacted by the substrat and the pH level of our reactors. Many samples were collected, analysed by flow cytometry and by the MiSeq sequencing technique.To follow the behaviour of the microbial communities, we focus our attention on the flow cytometric measurements, analyzed the pattern of the communities which were changing over time and sequenced communities and subcommunities of interest.