Definition (1):
Turbidostat is a device for maintaining microorganisms in continuous culture; it monitors cell density and regulates the dilution rate to maintain the cell density at a constant value.
Definition (2):
Bryson and Szybalski (1952) first introduced the turbidostat which combines some features of chemostats and serial dilution. Rather than including a new medium at a constant rate, in this device, cell density is kept constant. This is attained by a feedback loop which allows adjustment of the nutrient inclusion rate in response to fluctuations in density, generally measured through light transmittance. Now commercially, few of these devices can be seen, but they can be built applying modern microprocessor managed peristaltic pumps. These devices provide selection on maximal growth rate and at the same time maintain other conditions fixed or constant.
Definition (3):
A turbidostat refers to a continuing microbiological culture device like an auxostat or a chemostat, which possesses feedback between the culture vessel’s turbidity and the dilution rate. Theoretically, the relationship between growth in this device and growth in a chemostat is a bit complex, partially because they are similar. A chemostat has a constant volume and flow rate, and therefore a constant dilution rate. A turbidostat continuously adjusts the flow rate and thus the dilution rate to make the turbidity fixed.