Inorganic pyrophosphate as an energy source for ruminal bacteria

The ability of the predominant ruminal flora to utilize inorganic pyrophosphate as an energy source was examined. Rumen contents from steers fed diets containing pyrophosphate from 0%–0.13% of the diet dry matter were serially diluted and inoculated into (a) basal medium, no carbohydrates (BM); (b) basal medium plus pyrophosphate (0.05%) (BP); (c) basal medium plus carbohydrates (CM); and (d) basal medium plus carbohydrates plus pyrophosphate (0.05%) (CP). Growth was measured as increase in optical density. Addition of pyrophosphate to the CM medium reduced the maximum optical density by 36% and 98% in tubes inoculated with 10^–1 and 10^–3 dilutions of rumen contents, repectively. No growth occurred in pyrophosphate-containing media at dilutions higher than 10^–3. In vitro enrichment of bacteria growing on pyrophosphate did not increase the growth yield. These result indicate that the predominant ruminal bacteria do not utilize pyrophosphate as an energy source.