Summary auto-generated
This study examined how the rumen ciliate Entodinium caudatum metabolizes starch, maltose, and glucose. Using radioactively labeled sugars, researchers found that the protozoa incorporate glucose into intracellular pools as free glucose, maltose, and hexose phosphates, as well as into protozoal polysaccharides and intracellular bacteria. Sugar uptake occurred via both active processes (dominant at low concentrations) and passive processes (dominant at high concentrations). The protozoa hydrolyzed starch to maltose and glucose through enzymatic degradation. Notably, starch was most effective at prolonging protozoal survival, followed by maltose and glucose. The uptake rate of maltose exceeded that of glucose in equimolar concentrations, but both were markedly decreased by antibiotics. The study provided evidence for a permeability barrier between the protozoal ectoplasm and endoplasm, with the barrier being more permeable to maltose than glucose. Starch grains were engulfed and metabolized into volatile fatty acids (acetate and butyrate), but carbohydrates were not used for protozoal protein synthesis.
Key findings
- Entodinium caudatum hydrolyzed starch to maltose and glucose, which were then metabolized or liberated into the medium as volatile fatty acids (acetate 35%, butyrate 65%)
- Sugar uptake occurred through both active transport (predominant at low concentrations) and passive diffusion (predominant at high concentrations), suggesting a permeability barrier between the ectoplasm and endoplasm
- Starch was most effective at prolonging protozoal survival, followed by maltose and glucose; maltose uptake rate exceeded glucose uptake when present in equimolar concentrations
- Antibiotic treatment (penicillin and neomycin) markedly decreased the uptake rate of both glucose and maltose, suggesting intracellular bacteria contributed to sugar metabolism
- No evidence for protein synthesis from carbohydrates; instead, 14C from glucose was incorporated into a protozoal glucose polysaccharide and intracellular bacteria
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Abstract
SUMMARY: Washed suspensions of Entodinium caudatum grown in vitro and incubated anaerobically incorporated 14C from [14C]glucose into the cell pool as [14C]glucose, maltose and hexose phosphate and into protozoal polysaccharide and intracellular bacteria as a glucose polymer. The uptake of sugars into the pool was by an active process (predominant at low sugar concentrations) probably into the protozoal endoplasm, and by a passive process (predominant at high concentrations) into another part of the cell. Uptake of glucose by the active process was not sufficiently rapid to increase the level of glucose in the pool by more than 17% per hour; this was probably insufficient to increase appreciably the rate of glucose utilization. These protozoa hydrolysed starch to maltose and glucose and the level of these sugars in the pool of protozoa metabolizing starch grains was controlled in part by the inhibitory effect of these sugars on the enzymes that formed them. Studies on the enzymes involved in the metabolism of starch showed that the glucose in starch was hydrolysed to free glucose before phosphorylation. In experiments on the effect of carbohydrates on the survival of protozoa, starch was the most effective in prolonging protozoal life, followed by maltose and glucose in that order. The greater effectiveness of maltose was correlated with the finding that the rate of uptake of maltose carbon was always greater than that for glucose when the two sugars were present in equimolar concentrations. However, the rate for both sugars was markedly decreased in the presence of penicillin and neomycin. Evidence is presented that the protozoal ectoplasm may be freely permeable to sugars in the medium and that there is a barrier between the ectoplasm and endoplasm. 14C from [14C]starch grains was incorporated by the protozoa but there was no synthesis of protozoal protein from carbohydrate.