Cell growth in normal and synchronously dividing mass cultures of Tetrahymena pyriformis

Abstract

Tetrahymena pyriformis GL. was used for a study of growth based on distribution of cell size in mass cultures at optimal temperature (29 °C) and after intermittent temperature shocks inducing synchronous division. Samples were drawn at well defined stages of growth (Fig. 1). Cell size was estimated from the measurement of the major and minor cell axes. Division stages were considered separately. Volume classes are plotted in an equidistant scale in Fig. 2, and on log scale in Figs. 5 and 6. A 3-day-old test tube culture was always used as an inoculum. The cells from the inoculum are fairly big and not quite normally distributed with respect to size. They become normally distributed in the course of few hours of logarithmic growth and remain so up to the time of the negative growth acceleration phase. Development of nutrient deficiency tends to split the population into two parts which become united in the maximum stationary phase again. In eight generations of logarithmic growth the mean cell size is reduced about 50 per cent. During heat treatment the mean cell size is increased about 300 per cent. In the course of synchronous division steps, the mean cell size is reduced after 5 hours to the size which is found in the control cultures. The considerable change in mean cell size is not paralleled by striking changes of the coefficient of variation of the size distribution of the individual cells. Further analysis with the probit method revealed that the heat treatment produces a population with a distribution of cell sizes which deviates in a typical manner from normality. On a percentage basis, the small cells grow less than the big cells during heat treatment. The analysis of cell size distribution reveals similar reactions in test tube cultures and in cells exposed to temperature shocks in a well aerated culture.