Interplay between fermentative and respiratory energy conservation in ruminal Prevotella sp.

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Prevotella is a predominant genus in the rumen microbiome, there they are important for non-cellulose polysaccharide and protein degradation. Because of their metabolic activities, Prevotella maintain the redox potential in the rumen and balance the rumen microbial activities. So far, Prevotella spp. were mainly studied because of their carbohydrate active enzymes and the proteolytic properties. Reductive pathways including the generation of NAD+ and the overall redox balance were ignored in the past. A preliminary study of the applicants identified the presence of Na+ -translocating NADH:quinone oxidoreductase (NQR) proteins affiliated to Prevotella spp. in rumen samples. Another analyses using a pure Prevotella bryantii culture verified the presence of NQR as the major oxidoreductase in the respiratory chain of this organism. This capacity can be coupled to the reduction of fumarate. The NQR is the target for the ionophore monensin, which is largely used to prevent ketosis in the cattle and to reduce methane emission. As Prevotella were almost not considered to be influenced by the ionophore treatment before, the presence of the detected NQR strongly indicates a possible negative effect. Thus, in the collaborative research project, we aim to understand how NADH:fumarate oxidoreduction catalysed by the Na+ -NQR and the fumarate reductase contributes to energy generation during fermentation of aspartate or glucose by P. bryantii (project 1, J. Steuber). The obtained knowledge is used to interpret proteomic and metabolomic data with pure Prevotella cultures and rumen samples (project 2, J. Seifert). Our long-term goal is a complete reconstruction of the catabolic reactions of these important ruminal bacteria and to identify possible agents, which inhibit their growth in the rumen and result in an imbalanced rumen microbiome with negative effects to the animal.