13C-NMR Studies on Lactate Metabolism in a Porcine Gut Microbial Ecosystem

Lactate is seldom detected as a major acid in the hindgut because it is a typical intermediate metabolite and is converted to a short-chain fatty acid (SCFA) by lactate-utilizing bacteria. Lactate becomes a key metabolite in the large intestine when lactogenic and bifidogenic dietary supplements are fed to animals. If lactate-utilizers are eliminated, lactate will be accumulated. Accumulation of lactate in hindgut might be responsible for diarrhoea caused by short-bowel syndrome, dyspepsia, and antibiotic treatments. Thus, the lactate metabolism in the hindgut ecosystem is important. L-[3- 13 C]-lactate fermentation was studied in a pig in vitro model using 13 C-NMR. Pig cecal digesta were diluted with four weights of an anaerobic phosphate buffer containing 13 C-labeled lactate. The mixture was incubated for 24 h at 37°C with gentle shaking. A portion of the culture was sampled periodically and analysed for SCFA. [3- 13 C] propionate, [2- 13 C] acetate, [2- 13 C] propionate, [2- 13 C] butyrate, and [4- 13 C] butyrate were produced from [3- 13 C]-Lactate in decreasing order. The importance of an acrylate pathway in propionate formation was evidenced by the predominant [3- 13 C] propionate formation. An equal production of [2- 13 C] butyrate and [4- 13 C] butyrate, as well as a negligible production of [3- 13 C] butyrate, indicated that extra non-labeled acetate is required for butyrate synthesis. 13 C-labelled butyrate, together with the detection of [2- 13 C] valerate, suggested the important role for Megasphaera elsdenii in lactate utilization in the system.