Determination of cellular rate distributions in microbial cell populations: Feeding rates of ciliated protozoa

A novel procedure is proposed for determining distributions of rate properties and correlations of rate with state properties of microbial cell populations. The procedure is novel in that it uses transient data, and thus, it does not require that the population be in balanced growth, although it requires that the population structure does not change during the short transient experiment. The procedure is applied to populations of the ciliated protozoan Tetrahymena to determine ingestion rate variability. The number of ingested microspheres per cell and the single‐cell protein content—an indicator of cell size—were directly determined with dual‐color flow cytometry. The proposed technique revealed the correlation pattern of the particle ingestion rate with cell size. In particular, ingestion rate was found to be positively correlated with cell size for the smaller feeding cells and to be uncorrelated with size for the larger cells. Using the fact that particle uptake from dilute particle suspensions is a Poisson random process, we determined that the coefficient of variation of the distribution of ingestion rates within the feeding population is about 50%. It was concluded that the dynamics of particle ingestion can be accurately described only if it is realized that particle ingestion rates are distributed. © 1993 John Wiley & Sons, Inc.