Changes in DNA Content and Cellular Death during a Starvation-Survival Process of Escherichia coli in River Water

Abstract Four nucleoid staining procedures were compared during the starvation-survival process of Escherichia coli in river water. Only the method performed as a modification of the standard acridine orange direct procedure allowed us to visualize nucleoids during the 95 days of experimentation. Moreover, with this method the total number of cells and nucleoid-containing cells can be simultaneously enumerated. The decrease of the chromosomal DNA content of population and of the nucleoid-containing cells indicates that ghosts form and cellular death occurs throughout the starvation-survival process. A long time (<30 days) is needed for non-nucleoid-containing cells to appear in river water; plasmid DNA is also negatively affected by environmental stress. After 4 days of storage in river water, the need to increase the volume of lysed cells used for the plasmid band visualization as well as the decrease in the plasmid band intensity would indicate a decrease in the plasmid DNA content during the starvation-survival process. According to our results, both chromosomal and plasmid DNA content decrease during the starvation-survival process of E. coli in river water.