Substrate Preferences in Continuous Culture

We have seen earlier that cells will exhaust a desired substrate such as glucose before they bother to synthesize the enzymes needed for a less common substrate. The controlling factor is glucose concentration; cells use this as the switch. When glucose concentrations falls below the cell's setpoint, the ability to synthesize the enzymes for a different substrate is turned on. Of course, that substrate must be present to initiate this synthesis. We can see this with this exercise that plots concentrations at steady state:

Noteworthy features:

  • The vertical line shows the maximum specific growth rate.
  • At lower dilution rates, both sugars are consumed.
  • At higher dilution rates where the steady-state concentration of glucose rises, the uptake of lactose is turned off.
  • Yield coefficients and maintenance coefficients were assumed to be the same for these sugars. This is incorrect but probably changes the results only slightly.

     Go with the flow to Shifting Limitation