Question

Explain continuous fermentation process with respect to Chemostat and Turbidostat.

Answer 1

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Even a repeated fed-batch culture is a closed culture system in the sense introduced; the essential open culture system is the chemostat. A chemostat consists of a culture:

   into which fresh medium is continuously introduced at a constant rate, and

   the culture volume is kept constant by continuous removal of culture at the same rate, and

   in which the supply of a single nutrient controls growth rate.

The fermenter is called a chemostat because the growth rate is controlled by the availability of a single component of the medium (the limiting substrate). Important features are that it is the continuous introduction of fresh medium that feeds the limiting substrate to the culture and the dilution rate (that is, the rate of addition of fresh medium) determines the specific growth rate of the culture (Fig. 24) (Matteau et al., 2015).

A basic chemostat

Fig. 24. A basic chemostat. A, Sketch diagram of a continuous culture vessel. B, Record of biomass concentration (x) and substrate (glucose) concentration (S) over the early stages of a cultivation showing the transition from the initial batch phase to the continuous culture phase.

The main features of a chemostat culture are:

   Volume of the culture remains constant,

   The time required to mix a small volume of medium with the culture should be small, that is, it should approach perfect mixing,

   Environmental conditions can be maintained constant (these include nutrient concentration, pH, temperature, antibiotic concentration),

   Specific growth rate can be varied from just above zero to just below

   An environmental condition (pH, temperature, oxygen tension, etc.) can be varied whilst maintaining specific growth rate constant,

   Biomass properties such as macromolecular composition and functional characteristics can be maintained constant,

   Biomass concentration can be set (by altering the concentration of the limiting substrate in inflowing medium) and maintained constant, independently of

   Substrate-limited growth can be maintained indefinitely and this can offer relief of catabolic repression and induction of secondary metabolism at low substrate (glucose) concentration. When chemostat cultures are operated for a very long time the organism evolves (see below); indeed, chemostat cultures can be used to select mutants with particular physiological characteristics

Answer 2

Answer:

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