Isotrichid protozoa influence conversion of glucose to glycogen and other microbial products1

The goal of this in vitro study was to determine the influence of isotrichid protozoa (IP) on the conversion of glucose (Glc) to glycogen (Glyc) and transformation of Glc into fermentation products. Treatments were ruminal inoculum mechanically processed (blended) to destroy IP (B+, verified microscopically) or not mechanically processed (B-). Accumulated microbial Glyc was measured at 3 h of fermentation with (L+; protozoa + bacteria) or without (L- predominantly protozoa) lysis of bacterial cells in the fermentation solids with 0.2 N NaOH. Two 3-h in vitro fermentations were performed using Goering-Van Soest medium in batch culture vessels supplemented with 78.75 mg of Glc/vessel in a 26.5-mL liquid volume. Rumen inoculum from 2 cannulated cows was filtered through cheesecloth, combined, and maintained under CO2 for all procedures. At 3 h, 0.63 and 0.38 mg of Glc remained in B- and B+. Net microbial Glyc accumulation (and Glc in Glyc as % of added Glc) detected at 3 h of fermentation were 3.32 (4.69%), −1.42 (−2.01%), 6.45 (9.10%), and 3.65 (5.15%) mg for B-L-, B+L-, B-L+ and B+L+, respectively. Treatments B+ and L+ gave lower Glyc values than B- and L-, respectively. Treatment B+L- demonstrated net utilization of α-glucan contributed by inoculum with no net Glyc production. With destruction of IP, total Glyc accumulation declined by 44%, but estimated bacterial Glyc increased. Microbial accumulation of N increased 17.7% and calculated CH4 production decreased 24.7% in B+ compared with B-, but accumulation of C in microbes, production of organic acids or C in organic acids, calculated CO2, and carbohydrates in cell-free medium did not differ between B+ and B-. Given the short 3-h timeframe, increased N accumulation in B+ was attributed to decreased Glyc sequestration by IP rather than decreased predation on bacteria. After correction for estimates of C from AA and peptides utilized by microbes, 15% of substrate Glc C could not be accounted for in measured products in B+ or B-. Approximately 30% of substrate Glc was consumed by energetic costs associated with Glc transport and Glyc synthesis. The substantial accumulation of Glyc and changes in microbial N and Glyc accumulation related to presence of IP suggest that these factors should be considered in predicting profiles and amounts of microbial products and yield of nutrients to the cow as related to utilization of glucose. Determination of applicability of these findings to other soluble carbohydrates could be useful.