The concept is very simple; the medium is pumped continuously, and the volume is constant because the excess medium overflows. Most laboratory research uses glass bioreactors so that observation is easy. Peristaltic (tubing squeezer) pumps are commonly used because simple connections with tubing can include some extra tubing to be placed in the pump. Magnetic stirring almost always works well.

Some sources of concern are:

  1. foaming results in overflow with the volume of liquid not exactly constant,
  2. some very fragile cells are ruptured when caught between the magnetic stirring bar and the glass of the vessel. Suspending the stirring bar usually corrects this fault.
  3. changing pumping rate by turning the pump on and off over short time periods may not work because cells respond to sudden changes by altering their rates. Very short intervals of on/off are OK.
  4. bacteria travel upstream quite easily. They will reach the reservoir of sterile medium quickly unless the liquid path is interupted by an air break in which the medium falls in drops through air as shown in the sketch.

  5.  Go to turbidostat (go with the flow)
     Jump ahead to auxostat