Regulation of ribosome synthesis in Escherichia coli: effects of temperature and dilution rate changes.

The effect of temperature on the synthesis of ribosome in Escherichia coli K-12 was investigated. In continuous fermentation, the total and functioning ribosome contents decreased with increasing temperature, while the non-functioning ribosome content remained unchanged. Cells contained higher amounts of functioning ribosome at lower temperatures to compensate for the decrease in translational activity. A transient study was performed to investigate the dynamic response of the cell to changes in the dilution rate. In response to the dilution rate shift-up, the cell mass decreased until the cells produced a sufficient amount of ribosomes to support the new higher growth rate. However, the response to the dilution rate shift-down resulted in an immediate increase in cell mass. This may be due to the fact that the cell already contains enough ribosomes to support a lower growth rate corresponding to the new low dilution rate. Based on the experimental results, a mathematical model was developed to describe the cell growth at transient as well as steady states. The total ribosome content was included as a variable because it affects the growth rate of the cell.