RADIOCOBALT ACCUMULATION IN TETRAHYMENA

¹ Dept. of Biology, University of Buffalo, Buffalo 14, N. Y., and Biology Division, Oak Ridge National Laboratory

1. A steady uptake of radioactive cobalt was observed during the growth of Tetrahymena in synthetic medium. When the initially-added amount of cobalt was 3.7 µgm./ml., nearly 26% of the total was accumulated during 60 hours of growth. This amounted to approximately one billion atoms of cobalt per animal.

2. Upon reaching the stationary phase, sizable amounts of cobalt were released from the population. Fifty per cent release was observed in 36 hours with a rate amounting to 1.4 x 10^-6%/hour/organism.

3. The number of animals present had a definite effect on the accumulation of cobalt per animal. Populations of 10⁴ animals became nearly ten times as radioactive as populations containing two million organisms.

4. In nutritionally-deficient media, the release of cobalt was biphasic. The first was very rapid and took place within two hours. The initial rate of release of cobalt amounted to 13%/hour/organism. The second mechanism was much slower and amounted to 1.7%/hour/organism. Fifty per cent release was noticed in 20 hours under these conditions.

5. As the concentration of cobalt was varied, the rates of uptake increased rapidly. Concentrations higher than 1.85 µgm./ml. had little effect. The greatest absolute amount of cobalt was accumulated when 3.7 µgm./ml. was initially present in the medium, but the ability to concentrate this ion over that contained in the environment reached a peak at 0.37 µgm./ml. of cobalt ion.