Isotopomer Flux Analysis of Bifidobacterium ssp Carbohydrate Metabolism

Neil P. J. Price1, Anthondy Adeuya1, Terence R. Whitehead2, David A. Sela3, and David A. Mills3. USDA-ARS-NCAUR, 1Bioproducts & Biocatalysis Research Unit, and 2Fermentation Biotechnology Research Unit, 1815 North University Street, Peoria, Illinois 61604, and 3Department of Viticulture and Enology, University of California, Davis, CA 95616, USA

Bifidobacteria are gram-positive microorganisms widely applied in fermented dairy products due to their health-promoting effects. Biofobacterium ssp. may also represent up to 91% of microbial gut population in the infant colon, but considerably less in adults. Fructose-6 phosphate phosphoketolase (F6PPK) is a key enzyme of the so-called “bifid shunt”, a unique Bifidobacterium ssp. metabolic pathway involved in direct cleavage of fructose-6-phosphate to erythrose-4-phosphate and acetyl phosphate. Furthermore, bifodobacteria lack genes for glycolysis and gluconeogenesis pathways. Results of isotopic labeling experiments with 13C-fructose confirm that the bifid shunt is the predominant pathway for the degradation of carbohydrates by Bifidobacterium ssp., by-passing glycolysis. The fractional distribution of 13C into carbohydrate and fatty acid metabolites was analyzed by GC-EI-MS. The acetate derived from sugars via the bifid shunt is both secreted and incorporated into the Bifidobacterium de novo fatty acids. Moreover, several metabolic “chase” experiments have been undertaken using probiotic oligosaccharides, and human milk oligosaccharides, and differential pathways are reported for B. longum and B. infantis strains. These findings are consistent with the genome data for these strains, and suggest ways by which B. infantis has adapted to the environment of the infant human gut.