Effects of Protozoa and Glass Beads on Bacterial Biomass and Metabolism in a Food Chain System of Glucose-Pseudomonas sp. strain DP-4-Tetrahymena thermophila

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The effect of the protozoa Tetrahymena thermophila or glass beads on the biomass of the bacterium Pseudomonas sp. strain DP-4 and metabolism of glucose in a steady state was studied in a food chain system of glucose-Pseudomonas sp. strain DP-4-T. thermophila. Glucose was added to 1.5 ml cultures in 50 ml vials at a rate of 50 μg C/vial/day. In the 1.5 ml cultures without glass beads, the bacterial biomass was ca. 450 and 26 μg C/vial when the protozoa was absent and present, respectively. The bacterial biomass with glass beads was ca. 650 and 34 μg C/vial when the protozoa was absent and present, respectively. Protozoan biomass was 7 and 20 μg C/vial without or with glass beads, respectively. Irrespective of presence of the protozoa or glass beads, the rate of consumption of glucose per vial (50 μg C/vial/day) was considered to be almost the same as the rate of CO₂ evolution per vial (45-47 μg C/vial/day). The diameter of the glass beads (50, 70 or 100 μm) had no effect on the bacterial biomass in the absence of the protozoa. While, in the presence of the protozoa, the bacterial biomass was greatest when the diameter of glass beads was just 50 μm. These results suggested that the rate of glucose consumption per unit bacterial biomass of 0.11 μg glucose-C/μg biomass-C/day was increased to 1.9 μg glucose-C/ μg biomass-C/day by protozoan predation, while the value was decreased to 0.077 μg glucose-C/μg biomass-C/day by glass beads. The significance of protozoan predation and particles for bacterial biomass and metabolic activity was discussed.