Etude de Fibrobacter succinogenes en bioréacteur anaérobie en vue de la dégradation de déchets végétaux

The interest for biodegradation technologies of vegetation waste is increasingly significant, as well for an environmental point of view than a public health point of view. The two most important biotechnologies for vegetable degradation, based on biological events, are the biomethanogenesis and composting. The biotechnology developed in this study, is based on the efficiency of the rumen to degrade vegetables. Indeed, ruminants are the most efficient animals to degrade vegetable wastes thanks to a microbial community very abundant and very effective. Among these micro-organisms, Fibrobacter succinogenes is the major species. It has an enzymatic equipment very complete and complex which explain these capacities to degrade the vegetables. These potentialities can thus be used within the framework of the development of a technology of biodegradation of vegetation wastes and within the framework of the MELiSSA project which aims to create an artificial closed ecosystem. This study focused on the development of an anaerobic bioreactor for Fibrobacter succinogenes S85 cultures. First, cultures on glucose were carried out in order to validate the techniques used. These cultures showed that our process is valid for Fibrobacter succinogenes cultures. They also showed a link between VFA production, glucose consumption and gas pressure measurement. So the pressure could be used as a growth parameter especially when growth occurs on vegetables. The degradation of the vegetation wastes by Fibrobacter succinogenes was then performed. The substrate was composed of cabbage, wheat straw and soya bean, in mixture (1/3 of each) or separately. These cultures showed different kinetics of degradation according to the substrate used. The explanation is that the difference in composition of the substrate (cellulose, hemicellulose and lignin) causes, for the substrate richest in fibres, the synthesis of more specific enzymes. Then, the degradation of a substrate from a first degradation by methanogenesis, within the framework of MAP project, was carried out. These cultures allowed an improvement of the system and revealed important total degradation yields (MAP loop). The presence of a contaminant was verified by molecular biology in order to explain the production of butyrate in our cultures. With these experiments we can't conclude of the presence of a contaminant and other research must be performed. Finally, all performed fermentations were simulated with the program "Anaerobic Waste Compartment Modelling and Simulation". These simulations show a very great similarity with the experimental results. So this program can be used to predict the degradation of a biggest quantity of substrate.Les potentialités Fibrobacter succinogenes, l'espèce majeure du rumen, ont été utilisées pour la dégradation de végétaux et dans le cadre du projet MELiSSa créé par l'ESA. Dans un premier temps des cultures sur glucose nous ont permis de maîtriser notre procédé et de valider les techniques utilisées. Les cultures sur déchets végétaux (chou, soja et paille) par Fibrobacter succinogenes ont permis de mettre en évidence des cinétiques de dégradation différentes selon le substrat utilisé. Ensuite, les cultures sur un substrat issu d'une première dégradation par biométhanogenèse (projet MELiSSA), ont permis une amélioration du système et ont révélé des rendements de dégradation importants. La recherche d'un contaminant par biologie moléculaire a été menée pour expliquer la production de butyrate dans nos cultures. Enfin le programme "Anaerobic Waste Compartment Modelling and Simulation" nous a montré une très grande similitude avec les résultats expérimentau