Growth-Inhibitory Activities in Tetrahymena Culture Medium of the Stationary Phase

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Culture medium in the stationary phase of Tetrahymena pyriformis (strain W) had activities to reduce the growth rate of the ciliate markedly, while the culture medium in the logarithmic phase had no growth-inhibitory activities. These activities were heat stable and reduced by dialysis against a fresh culture medium. When the pH of the culture medium in the stationary phase (pH 7.4) was changed to that of fresh culture medium (pH 6.5), the growth rate of the ciliate was recovered. Further, when the pH of the fresh culture medium (pH 6.5) was changed to that of the culture medium in the stationary phase (pH 7.4), the growth rate of the ciliate was reduced. These results suggest that the pH in the culture medium has very important roles for cell growth.