Growth requirements of a new food-vacuole-less mutant of Tetrahymena.

The growth requirements of the ciliate Tetrahymena thermophila have been known for a long time. In this study we have investigated the additional requirements induced in a cell line defective in phagocytosis. The mutant cell line of T. thermophila, II 8 G, derived from the wildtype, T. thermophila, CU 399, has apparently no oral structures and forms no food vacuoles at 37°C, but has normal oral structures and the ability to form food vacuoles at normal rates at 28°C. Taking advantage of a synthetic nutrient medium, we observed that the mutant cell line shows increased requirement for Fe(III), Cu(++) and folic acid under restrictive conditions. Phagocytosis obviously plays a role in utilization of low concentrations of the three substances, whereas all other required substances can enter fast enough to support short generation times.