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Four bifidobacteria, each representing a cluster of strains with specific inulin-type-fructan degradation capacities, were grown in coculture fermentations with Bacteroides thetaiotaomicron LMG 11262, a strain able to metabolize both oligofructose and inulin. In a medium for colon bacteria with inulin as the sole added energy source, the ability of the bifidobacteria to compete for this substrate reflected phenotypical variation. Bifidobacterium breve Yakult, a strain that was not able to degrade oligofructose or inulin, was outcompeted by B. thetaiotaomicron LMG 11262. Bifidobacterium adolescentis LMG 10734, a strain that could degrade oligofructose (displaying a preferential breakdown mechanism) but that did not grow on inulin, managed to become competitive when oligofructose and short fractions of inulin started to accumulate in the fermentation medium. Bifidobacterium angulatum LMG 11039(T), a strain that was previously shown to degrade all oligofructose fractions simultaneously and to be able to partially break down inulin, was competitive from the beginning of the fermentation, consuming short fractions of inulin from the moment they appeared. Bifidobacterium longum LMG 11047, representing a cluster of bifidobacteria that shared both high fructose consumption and oligofructose degradation rates and were able to perform partial breakdown of inulin, was the dominating strain in a coculture with B. thetaiotaomicron LMG 11262. These observations indicate that distinct subgroups within the large-intestinal Bifidobacterium population will be stimulated by different groups of prebiotic inulin-type fructans, a variation that could be reflected in differences concerning their health-promoting effects.