ANALYSIS OF CELL-SIZE AND DNA CONTENT IN EXPONENTIALLY GROWING AND STATIONARY-PHASE BATCH CULTURES OF ESCHERICHIA-COLI

Escherichia coli strains were grown in batch cultures in different med ia, and cell size and DNA content were analyzed by flow cytometry, Ste ady-state growth required large dilutions and incubation for many gene rations at low cell concentrations. In rich media, both cell size and DNA content started to decrease at low cell concentrations, long befor e the cultures left the exponential growth phase. Stationary-phase cul tures contained cells with several chromosomes, even after many days, and stationary-phase populations exclusively composed of cells with a single chromosome were never observed, regardless of growth medium. Th e cells usually contained only one nucleoid, as visualized by phase an d fluorescence microscopy. The results have implications for the use o f batch cultures to study steady state and balanced growth and to dete rmine mutation and recombination frequencies in stationary phase.