Bifidobacterium pseudolongum in the Ceca of Rats Fed Hi-Maize Starch Has Characteristics of a Keystone Species in Bifidobacterial Blooms

This study addresses the microbiology and function of a natural ecosystem (the rat gut) using DNA-based observations and in vitro experimentation. The microbial community of the large bowel of animals, including humans, has been studied extensively through the use of high-throughput DNA sequencing methods and advanced bioinformatics analysis. These studies reveal the compositions and genetic capacities of microbiotas but not the intricacies of how microbial communities function. Our work, combining DNA sequence analysis and laboratory experiments with cultured strains of bacteria, revealed that the increased abundance of bifidobacteria in the rat gut, induced by feeding indigestible starch, involved a species that cannot itself degrade the starch ( Bifidobacterium animalis ) but cohabits with a species that can ( Bifidobacterium pseudolongum ). B. pseudolongum has the characteristics of a keystone species in the community because it had low abundance but high ability to perform a critical function, the hydrolysis of resistant starch.