Two Routes of Metabolic Cross-Feeding betweenBifidobacterium adolescentisand Butyrate-Producing Anaerobes from the Human Gut

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Abstract
Dietary carbohydrates have the potential to influence diverse functional groups of bacteria within the human large intestine. Of 12Bifidobacteriumstrains of human gut origin from seven species tested, four grew in pure culture on starch and nine on fructo-oligosaccharides. The potential for metabolic cross-feeding betweenBifidobacterium adolescentisand lactate-utilizing, butyrate-producingFirmicutebacteria related toEubacterium halliiandAnaerostipes caccaewas investigated in vitro.E. halliiL2-7 andA. caccaeL1-92 failed to grow on starch in pure culture, but in coculture withB. adolescentisL2-32 butyrate was formed, indicating cross-feeding of metabolites to the lactate utilizers. Studies with [13C]lactate confirmed carbon flow from lactate, via acetyl coenzyme A, to butyrate both in pure cultures ofE. halliiand in cocultures withB. adolescentis. Similar results were obtained in cocultures involvingB. adolescentisDSM 20083 with fructo-oligosaccharides as the substrate. Butyrate formation was also stimulated, however, in cocultures ofB. adolescentisL2-32 grown on starch or fructo-oligosaccharides withRoseburiasp. strain A2-183, which produces butyrate but does not utilize lactate. This is probably a consequence of the release byB. adolescentisof oligosaccharides that are available toRoseburiasp. strain A2-183. We conclude that two distinct mechanisms of metabolic cross-feeding betweenB. adolescentisand butyrate-forming bacteria may operate in gut ecosystems, one due to consumption of fermentation end products (lactate and acetate) and the other due to cross-feeding of partial breakdown products from complex substrates.