Inulin-type fructan degradation capacity of Clostridium cluster IV and XIVa butyrate-producing colon bacteria and their associated metabolic outcomes

Four selected butyrate-producing colon bacterial strains belonging to Clostridium cluster IV (Butyricicoccus pullicaecorum DSM 23266(T) and Faecalibacterium prausnitzii DSM 17677(T)) and XIVa (Eubacterium hallii DSM 17630 and Eubacterium rectale CIP 105953(T)) were studied as to their capacity to degrade inulin-type fructans and concomitant metabolite production. Cultivation of these strains was performed in bottles and fermentors containing a modified medium for colon bacteria, including acetate, supplemented with either fructose, oligofructose, or inulin as the sole energy source. Inulin-type fructan degradation was not a general characteristic among these strains. B. pullicaecorum DSM 23266(T) and E. hallii DSM 17630 could only ferment fructose and did not degrade oligofructose or inulin. E. rectale CIP 105953T and F. prausnitzii DSM 17677(T) fermented fructose and could degrade both oligofructose and inulin. All chain length fractions of oligofructose were degraded simultaneously (both strains) and both long and short chain length fractions of inulin were degraded either simultaneously (E. rectale CIP 105953(T)) or consecutively (F. prausnitzii DSM 17677(T)), indicating an extracellular polymer degradation mechanism. B. pullicaecorum DSM 23266(T) and E. hallii DSM 17630 produced high concentrations of butyrate, CO2, and H-2 from fructose. E. rectale CIP 105953T produced lactate, butyrate, CO2, and H-2, from fructose, oligofructose, and inulin, whereas F. prausnitzii DSM 17677(T) produced butyrate, formate, CO2, and traces of lactate from fructose, oligofructose, and inulin. Based on carbon recovery and theoretical metabolite production calculations, an adapted stoichiometrically balanced metabolic pathway for butyrate, formate, lactate, CO2, and H-2 production by members of both Clostridium cluster IV and XIVa butyrate-producing bacteria was constructed.