Distribution of Cell Size in Growing Cultures of Bacteria and the Applicability of the Collins-Richmond Principle

Abstract

SUMMARY: Theoretical cell-size distributions for populations of growing cells are calculated for different models of cell growth and for different degrees of variability in size of cells at division. From these computations, it is concluded that the coefficient of variation (c.v.) is almost independent of the relationship of growth rate to cell size. It is 20% if there is no variability in the cell size at division. For a case typical for enteric rod-shaped bacteria, the variability in cell size at division is about 10% and the calculated c.v. in cell size of the population in this case increases to 22-23%. Calculations based on the microscopic observations of others are in the range of 20-25%. It is proposed that the c.v. of the size distribution serve as a standard in assessing the accuracy of the electronic instruments that size bacteria. Evidently, only the higher moments of the population cell size distribution contain information bearing on the growth dependence of the organisms on their size. It is pointed out that this means that the Collins-Richmond principle must be applied only to precise and accurate data.