Difference Between Chemostat and Turbidostat

The main difference between chemostat and turbidostat is that in chemostat, a constant chemical environment is maintained whereas, in turbidostat, a constant turbidity is maintained. To do that, the fresh medium is continuously added to the chemostat at the same rate as the products are removed while in turbidostat, the fresh media is automatically added to the culture maintaining a constant turbidity. 

Chemostat and turbidostat are two types of continuous cultures, which are open systems.  

Key Areas Covered 

1. What is a Chemostat
     – Definition, Facts, Importance
2. What is a Turbidostat
     – Definition, Facts, Importance
3. What are the Similarities Between Chemostat and Turbidostat
     – Outline of Common Features
4. What is the Difference Between Chemostat and Turbidostat
     – Comparison of Key Differences

Key Terms

Cell Density, Chemostat, Dilution Factor, Limiting Nutrient, Turbidostat

What is a Chemostat 

Chemostat is a type of continuous culture in which a constant chemical environment is maintained throughout the process. This means fresh medium is added to the culture continuously while removing the product. Dilution rate is the rate of nutrient exchange, which is constant in a chemostat.

Figure 1: Chemostat

Also, a chemostat proceeds with a limiting nutrient in the culture. The limiting nutrient is one of the essential nutrients for the growth of microorganisms. When microorganisms get this nutrient in a limiting concentration, the cell density of the medium depends on the concentration of the limiting nutrient. 

What is a Turbidostat 

Turbidostat is the other type of continuous culture in which a constant turbidity is maintained within the culture. Cell density determines the turbidity of the medium. Hence, the cell density of the culture is maintained at a constant value. In order to maintain a constant cell density, the rate of the addition of nutrient is changed by continuously measuring the cell density of the culture. The cell density is measured by measuring the light transmittance of the culture.

Figure 2: Industrial Fermenter 

Since the cell density of the culture is constant, turbidostat is also called a biostat.

Similarities Between Chemostat and Turbidostat

• Chemostat and turbidostat are two types of continuous cultures. 
• Both are open systems. 
• Fresh medium is added to the culture while removing the products throughout the process. Hence, both systems maintain a constant volume. 
• Both cultures exhibit a steady-state growth. 

Difference Between Chemostat and Turbidostat 

Definition 

A chemostat refers to a system in which the chemical composition is kept at a controlled level for the culture of microorganisms while a turbidostat refers to a continuous microbiological culture device, which has feedback between the turbidity of the culture vessel and the dilution rate. 

Constant Factor 

The chemical composition of the medium is constant in the chemostat while turbidity of the medium is constant in the turbidostat. 

Process 

Fresh medium is continuously added to the chemostat at the same rate as the products are removed while fresh media is automatically added to the turbidostat maintaining a constant turbidity.  

Dilution Rate 

Dilution rate remains constant in chemostat while dilution rate varies in the turbidostat. Also, a chemostat operates at a low dilution rate while the turbidostat operates at high dilution rates. 

Limiting Nutrient 

A chemostat proceeds with a limiting nutrient while a turbidostat has no such limiting nutrient.  

Conclusion 

Chemostat operates at a constant chemical environment. Thus, the rate of addition of fresh medium is equal to the rate of removal of the products. On the other hand, turbodistat operates at a constant turbidity. Turbidity is the cell density of the culture, which is measured by the light transmittance. The rate of addition of nutrients changes depending on the cell density. The main difference between chemostat and turbidostat is the type of conditions maintained constantly in each type of continuous culture. 

Reference:

1. Ziv, Naomi, et al. “The Use of Chemostats in Microbial Systems Biology.” Advances in Pediatrics., U.S. National Library of Medicine, 2013, Available Here    
2. “Turbidostat.” Egyptian Journal of Medical Human Genetics, Elsevier, Available Here    

Image Courtesy:

1. “Chemostat Vessel Diagram” By CGraham2332 – Own work (CC BY-SA 4.0) via Commons wikimedia    
2. “BTEC Bioreactors” By RickLawless (talk) (Uploads) – Own work (CC BY 3.0) via Commons Wikimedia