External factors limiting the multiplication potential of Tetrahymena.

By variation of nutritional and other external conditions we have determined the factors that limit the multiplication rate and the culture growth in Tetrahymena thermophila. The enriched synthetic medium of Kidder & Dewey (1951), a culture temperature of 29 degrees C, and aeration by agitation were chosen as reference conditions. The final cell density is increased by and proportional to the amount of the complete set of nutrients. Testing single nutritional factors or groups of them revealed that only nitrogen sources yield higher cell densities. But none of them or any combination is as capable of increasing the cell density as the complete medium. Therefore, the medium has to be considered as well balanced. Ammonia, cell density, O2 supply, and pH have been excluded as factors limiting the capacity for multiplication. There are no known factors promoting or inhibiting culture growth.