Microbiome shaping for enhanced production of medium chain carboxylic acids from brewer’s spent grains and H2+CO2 as substrates

Brewer’s Spent Grains (BSG) is the main by-product of breweries. It can be biologically valorised into Medium Chain Carboxylic Acids (MCCAs) via a multi-step fermentation using reactor microbiomes. The GEBI laboratory succeeded to produce MCCAs with reactor microbiomes fed with BSG and H2+CO2 as substrates. They showed that the use of H2+CO2 gas mixture enhances the MCCAs production. This work aimed to investigate if shaped microbiomes further enhance the MCCAs production from BSG and H2+CO2, compared to non-shaped microbiomes. Shaped microbiomes are microbiomes which already converted BSG and H2+CO2 into MCCAs in a previous process. Batch reactors filled with a microbiome (shaped or not) and H2+CO2 (77/23% (v/v) at 1.6 bar) were performed with (raw BSG or Acidogenic Liquor (AL)) or without organic substrate. The AL was specifically produced via an acidogenic fermentation of raw BSG. The AL was used autoclaved (twice 1h at 121°C with 8h at 4°C in between) or not. Better kinetics of MCCAs production were only possible with shaped microbiomes fed with raw BSG, but the MCCAs net productions were never significantly higher. The use of AL rather than raw BSG didn’t enhance the MCCAs production. Nevertheless, it interestingly increased (by at least 3) the net production of valeric acid. The use of non- autoclaved AL led to a MCCAs net production 25% higher than with the autoclaved AL. Regarding the MCCAs production from only H2+CO2 as substrates, it was possible with shaped microbiomes, but 38 days were needed to start. The results demonstrated that playing on the shaping of microbiomes is not a key element to highly enhance the MCCAs production while playing on the type of substrate is a key to consider to influence the production. This master’s thesis also aimed to identify the adequate conditions of storage to keep the MCCAs production activity of shaped microbiomes. Shaped microbiomes were stored at 4°C or -22°C, with O2 or H2+CO2 or N2 as storage atmosphere, for 2-21 days. The results showed that: the storage at 4°C is adapted to keep the MCCAs production activity, no precautions for the storage atmosphere are needed because it doesn’t influence the production, keeping shaped microbiomes 7-14 days interestingly enhances all the net productions.