抄録
It has been generally believed that isogenic cells in the culture systems are homogeneous. However, recent studies pointed out that a heterogeneous population may emerge and exist in the system. In this study to investigate cell population dynamics in a continuous culture of Escherichia coli, a glutamine synthetase gene (glnA) deficient mutant of E. coli YMC21 was used as a host. The plasmid pKGN-EGFP, carrying the fusion gene of glnA and egfp (enhanced green fluorescent protein, clontech) was introduced into YMC21. A minimal medium, containing glucose and glutamate as sole carbon and nitrogen sources, respectively, was used for the continuous culture of the strain. The changes in GFP intensity and forward scattering on the log scale were measured by the flow cytometry, when glutamate concentration in the feeding medium was changed. In the steady state of the culture, the cell population seemed to consist of two subpopulations of GFP intensity. According to the decrease of glutamate concentration, cell density also decreased. During this phase, the subpopulation with a high GFP fluorescence intensity became the major group in the system. On the other hand, when the glutamate concentration increased, cell concentration increased too. During the phase, the subpopulation which had a low GFP fluorescence intensity became the major group in the system. Interestingly, the subpopulation with the high or low GFP fluorescence intensity was not maintained, and the original distribution of the cell population emerged after reaching the steady state. By clarifying the role of each cluster or population of cells, the cell-cell interaction and interconnection was discussed in the future experiments.
