Résumé
Dark fermentation is a biological process involving complex microbial consortia which can degrade various complex wastes. It can be applied to lignocellulosic biomass after harvesting or food processing. During the fermentation process, the biomass is converted into several chemicals: organic acids (acetate, butyrate), solvents (ethanol), and hydrogen. This latter is a clean energy carrier which has an energy density 2.4 times higher than the other common fuels per unit of weight, with the advantage to produce only water after combustion. Previous results showed the possibility of producing H2 from complex biomass but with a low stability of continuous processes. The aim of this work is to understand how the history of several microbial inocula coming from natural environment can impact the fermentation process according to different fractions of lignocellulose (mono or polymeric forms). Batch fermentation tests of glucose, cellobiose, semi-amorphous cellulose, microcrystalline cellulose, arabinose, xylose, xylane, alkaline lignin and wheat straw were conducted in four replicates and with 4 different inocula (manure, aerobic sludge, anaerobic sludge and rabbit rumen). Results show that the variability of the fermentative pathways was closely linked to the history of inoculum. In addition, the overall conversion yield and the metabolic patterns were very dependent of the nature of the substrate whatever the inoculum. The type of carbohydrates (C6 or C5) but also its degree of polymerisation contributed both to the change in metabolite pattern. Microbial community analysis by SSCP and sequencing (work in progress) will give a deeper understanding on microbial traits that influenced the fermentation process, either because of metabolic shifts or microbial community changes. This work brings new elements on the mechanism of organic matter biodegradation by fermentation with mixed culture. It opens new possibility to propose fermentation improvement by a better management of fermentative microbial communities.