Growth during the bacterial cell cycle: analysis of cell size distribution.

Cell volume distributions were determined electronically for steady-state cultures of Escherichia coli, Bacillus megaterium, Bacillus subtilis, and Salmonella typhimurium by use of a Coulter transducer-multichannel analyzer system of good resolution. All of the cell volume distributions had the same general shape, even though cultures were grown at widely different rates. Some results were independent of any particular growth model. Both the variability in the volumes of dividing cells and the fraction of constricted and unseparated doublet cells increased with growth rate. The greater separation to single cells at slow growth rates is in agreement with the general finding that filamentous and hyphal forms are greatly reduced in slowly growing chemostat cultures. The distributions were fitted equally well by simple models which assumed that cell growth was either linear or exponential throughout the entire cell cycle. It is concluded that methods of determining growth rate by analysis of distributions of bacterial volumes do not yet have sufficient resolution to distinguish between a variety of alternative models for growth of bacteria.