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.
- 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.