Introductory Microbiology

Continuous cultures

 
• In a liquid batch culture, cells grow in a continuously changing environment with the result that the composition of the cells and the growth rate will be constantly changing. Novick and Szillard in 1959, devised a method called chemostat, which permits growth at a constant rate. In this apparatus fresh medium flows into a growth chamber at a carefully controlled rate. The volume of the culture is maintained by controlling the rates of inflow and outflow. The rate of growth is then controlled by regulating the inflow rates. In a chemostat therefore, indefinite growth at any constant rate can be maintained.

• The development of chemostat has allowed measurement of growth rates of microorganisms under a variety of conditions.
  The rate of loss of cells through the over flow can be expressed as dM / dt = F/V = DM
  Where F is flow rate, V is culture volume / hr, D is dilution rate.
  In a continuous culture, KM = DM
  K =D where, K is growth rate, D is dilution rate.
  Continuous culture methods are extremely useful both for genetic and biochemical studies.
• The Turbidostat is one in which growth is monitored by controlling and monitoring the turbidity of culture. By this, a culture of constant turbidity can be maintained. In a Photostat, which is used to get steady state cultures of photosynthetic organisms, growth rates can be controlled by controlling the light supply.

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