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The continuous cultivation of microbes is one of the methodology of growing significance [72]. This methodology is primarily characterized by constant microbial growth in continuous culture, i.e. a constant rate of growth in a constant environment. In continuous culture, parameters such as pH, substrate concentrations, metabolic products, and oxygen that eventually shift during the “batch cultivation” growth cycle are all constant; however, the experimenter may individually monitor and control them [73–75]. These attributes of the continuous culture method make it a desirable option for research while offering the industrial microbiologist several benefits in terms of more affordable production techniques (Figure 3.3).

Figure 3.3 Diagrammatic presentation of one stage and two stage fermentation process for biosurfactant production.

The continuous culture of microbes is performed in bioreactors called chemostats [76]. Chemostat is a type of bioreactor to which freshly prepared substrate is constantly supplied, while culture liquid comprising remaining nutrients, microbial end products, and microbe culture is continually withdrawn simultaneously at the same rate to maintain a constant culture volume. By adjusting the rate at which freshly prepared culture medium is supplied to the bioreactor, the specific growth rate of microorganisms can be effectively managed under limits [77, 78].

There may be several types of the continuous bioreactor, for example:

1 Auxostat: An auxostat is a method that uses inputs from a microbial growth chamber analysis to monitor the constant media flowrate, keeping the calculation at a constant level [79].

2 Retentostat: Retentostat is a modified form of chemostat in which a filtration assembly is linked to the effluent line and thus recycles the biomass to the bioreactor [19].

3 Turbidostat: A turbidostat is a continuous cultivation system with input on the optical density and dilution rate of the culture vessel [80].