Growth Kinetics in Liquid Media: Continuous Culture

An alternative to the liquid batch culture system is CONTINUOUS CULTURE in a liquid medium:

  • This involves the CONTINUOUS ADDITION OF FRESH CULTURE MEDIUM to the vessel and the WITHDRAWAL (by means of an overflow devise) of a corresponding volume of OLD, SPENT MEDIUM, which will contain some of the microbial cells.
  • The apparatus used is called a CHEMOSTAT.
Chemostat:
Diagrammatic representation of a chemostat.
  • Many environmental factors (e.g. pH, oxygen levels, nutrients and temperature) can be controlled very precisely throughout the incubation period.
  • The culture is stirred continuously - ensuring nutrients and oxygen reach the cells and metabolic products are distributed away from them.
  • Chemostats may be used to culture yeasts or mycelial fungi.
  • When culturing a mycelial fungus, the stirrer consists of blades which prevent large mycelial pellets from forming. [QUESTION: Why might this be important? ANSWER]
  • In this system the fungus continues GROWING EXPONENTIALLY because it's continuously supplied with fresh nutrients and oxygen, and the pH is controlled.
  • But the actual RATE OF THAT EXPONENTIAL GROWTH will depend upon the RATE OF FLOW OF THE CULTURE MEDIUM through the culture vessel, i.e. the DILUTION RATE.
  • The rate of exponential growth = specific growth rate = µ = dilution rate D.
  • µ = D = f/v, where f = flow rate (mlh-1) and v = volume of the culture (ml).
  • If all environmental factors are optimal for growth then the maximum specific growth rate (µmax) will be achieved.

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