Cell https://doi.org/10.1016/j.cell.2019.08.011 (2019)

Fiber-based dietary interventions can sustain beneficial microbiota. In Cell, Gordon and colleagues characterize the dietary fibers that selectively increase the fitness of the Bacteroides species in the human microbiota. In germ-free mice colonized with consortia of bacterial strains from a lean human donor and fed low-fiber diets supplemented with combinations of fiber preparations from diverse plant sources, particular fiber types have pronounced effects on specific Bacteroides species: pea fiber expands B. thetaiotaomicron; barley bran expands B. ovatus; and citrus pectin expands B. cellulosilyticus. In the respective Bacteroides species, most proteins induced are encoded by polysaccharide utilization loci and are involved in metabolism of the most abundant polysaccharide in these fibers (arabinan in pea fiber, and galacturonan in citrus pectin). B. cellulosilyticus and B. vulgatus compete for arabinan and galacturonan, with the former always suppressing the latter. B. cellulosilyticus and B. ovatus compete for arabinoxylan in the basal low-fiber diet, but the latter displays metabolic flexibility to mitigate competition. These results can inform efforts to enrich beneficial microbiota.