SETO, Masayuki and Tadayoshi TAZAKI (Dept. Plant Protection, Fac. Agri., Tokyo Univ. of Agri. and Tech.) Carbon dynamics in the food chain system of glucose-Esclerichia coli-Tetrahymena vorax. Jap. J. Ecol. 21,179-188 (1971) Applying the food chain system of organic compound (glucose), bacterium (Escherichia coli) and protozoa (Tetrahymena vorax) as a representative free-swimming unicellular predator, the carbon balance and the yield efficiency of the protozoa were studied, laying stress upon the dynamics of carbon from the ecological point of view. When the protozoa was cultured monoxenically in the medium in which washed suspension of E.coli was the sole source of carbon, the formation of the protozoa, evolution of CO_2 and excretion of the waste products increased as the substrate bacterium decreased, and at the time when the growth of protozoan population just reached the stationary phase, the efficiency of yield of the protozoa to the decrease of the bacteria, together with the evolution of CO_2 and the excretion of the waste products (particulate, soluble) were, respectively, 0.2,0.3 and 0.5 (0.3,0.2), in terms of carbon. From the growth curve of T.vorax and the decrease of E.coli, it was estimated that for formation of a new cell of the protozoa, ca.4×10^4 cells of the bacteria were ingested. The growth rate of T.vorax at the exponential phase feeding upon E.coli was 0.40 hr^<-1>, with the generation time of 2.50 hrs., under aerobic condition at 25℃. At different initial concentration of the bacterium (10-250 ppm-C), the growth curves of the protozoa showed the same type and the growth rate (0.40 hr^<-1>), and differed only in final yield proportionally, i.e., the efficiency of the yield of the protozoa-C (0.2) to the decrease of the bacteria-C and the evolution of CO_3-C (0.3), together with the excretion of the waste products-C (0.5), were almost the same irrespective of the different concentration of the bacterium ; but at the lowest bacterial concentration (2.5 ppm-C) slight inhibition both in the growth rate and in the yield efficiency was noted. Further, the numbers of the bacterial cells remained in the medium at the stationary phase of the protozoan growth were almost the same irrespective of the difference of the initial concentrations of the bacterium (4.2×10^7-4.2×10^9 cells/ml.) and showed ca. 1.8×10^7 cel1s/ml. It seems probable that T.vorax has no ability to ingest the bacterium less than the order of 10^7 cells per ml. Different culture temperature (17-28℃) did not affect the carbon balance, and altered only the growth rate (0.18 hr^<-1> at 17℃, 0.40 at 25℃ and 0.44 at 28℃). At the highest culture temperature (33℃) no growth occurred. The rate of CO_2-C evolution per unit biomass-C of T.vorax per hour at the exponential phase was estimated to be 0.2. As the biogeochemical agent, the role of the bacterial and protozoan populations in the turnover of material and mineralization of organic compounds were also discussed by a diagram of carbon flow for the relevant food chain system.
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