Levan degradation by fecal microbiota

Eleven fecal samples from healthy donors were incubated in phosphate-buffered defined medium with or without levan supplementation and varying presence of amino acids. The generation of heat, changes in pH and microbiota composition range and concentrations of produced and consumed metabolites during the growth were determined. The composition of fecal microbiota and profile of formed metabolites changed in response to substrate (levan and amino acids) availability. The main products of levan metabolism were acetic, lactic, butyric, propionic and succinic acids and carbon dioxide. Associated growth of levan-degrading (e.g. Bacteroides) and butyric acidproducing (e.g. Faecalibacterium) taxa were observed in levan-supplemented media. The study shows that the capacity of levan and possibly also other dietary fibers/ prebiotics to modulate the composition and function of colon microbiota can be predicted by using isothermal microcalorimetry linked to metabolite and consortia analyses.