To evaluate the extent to which single-cell glucose uptake rates determine the overall specific growth rate of a culture, dilute chemostat cultures of Escherichia coli BL21 were grown in defined medium under glucose limitation. The glucose uptake dynamics of the cell population was examined at the single-cell level using the fluorescent glucose analog, 2-NBDG. Between dilution rates of 0.12 h-1 and 0.40 h-1, mean cellular protein content and steady-state, extracellular glucose concentrations increased with increasing dilution rate. However, the distribution of 2-NBDG uptake rates in the population remained constant over the range of dilution rates studied. This indicates that the growth of cells in continuous culture is not limited by the maximum rate of uptake of glucose but by the availability of glucose for transport. The work represents an example of how quantitative flow cytometry can be applied to gain detailed insight into microbial growth physiology. (C) 2000 Elsevier Science B.V.
Bibliographical noteFunding Information:
We thank the National Science Foundation (BES-9708146) for partially supporting this work. We thank H. Matsuoka for kindly providing 2-NBDG. We are grateful for helpful discussions and suggestions provided by Thomas Egli, EAWAG and ETH, Dübendorf, Switzerland.
- Chemostat cultures
- Escherichia coli
- Glucose uptake rate
- Growth rate
- Single cells