Relation between Multiplication Rate and Temperature in Tetrahymena pyriformis, Strains HS and GL

SUMMARY. The multiplication rate of Tetrahymena pyriformis HS in proteose peptone medium was measured at 12 temperatures between 18.4°C. and 36.6°C. At the temperature optimum, 32.5°C., the generation time is 2.25 hours. The upper lethal temperature lies between 36.6°C. and 38.0°C. Similarly, a study of Tetrahymena pyriformis GL revealed a temperature optimum for multiplication of 29°C. with a generation time of 3.70 hours. The upper lethal temperature falls between 34.6°C. and 35.4°C. At all temperatures employed the HS strain of organisms multiplies more rapidly than strain GL. Under identical conditions, the two strains have distinctly different growth optima, upper lethal temperatures and growth rates. As measured by multiplication rate the readjustment to a sudden change in temperature (from 18.4°C. to 27.7°C.) is completed very rapidly, with an effective lag time of about 1 hour. Such a shift in temperature gives rise to a small degree of division synchrony during the first and second population doublings which follow. Subsequently, all traces of division synchrony are lost.