FEEDING HETEROGENEITY IN CILIATE POPULATIONS - EFFECTS OF CULTURE AGEAND NUTRITIONAL STATE

We have used a novel approach in conjunction with flow cytometry to qu antify the biological heterogeneity of populations of the ciliate Tetr ahymena pyriformis. It was found that the rate of particle uptake of e xponentially growing cells is not uniform among cells and partially co rrelated with cell size. The physiological state and growth history of the culture was found to affect to a large degree the population's fe eding heterogeneity. Stationary phase populations exhibited more unifo rm feeding behavior, as cell aging affects all cells and effectively r educes their ability to feed. Cells that were removed from the growth medium and resuspended in nonnutritive medium exhibited a more heterog eneous feeding behavior. The starved cells were stimulated to feed at considerably higher rates, and the stimulatory effect was more pronoun ced for larger cells. It is therefore demonstrated that population het erogeneity has to be evaluated in conjunction with the populations gro wth state as it is determined by the history of the population's growt h and nutritional state. (C) 1994 John Wiley and Sons, Inc.