Key Difference – Batch vs Continuous Culture
Microorganisms such as bacteria and fungi are very beneficial to various types of industries. For industrial usage, microorganisms should be grown in large scale during the fermentation process in order to extract the necessary products resulting from the microbial metabolism. A special apparatus called industrial fermenter is used to cultivate and maintain microbial biomass. It is a large vessel designed to provide space and necessary requirements for microbial growth and metabolism. There are two types of industrial fermentation cultures commonly adopted in industries named batch culture and continuous culture. The key difference between batch culture and continuous culture is that batch culture is a technique used to grow microorganisms under limited nutrient availability in a closed system while continuous culture is a technique used to grow microorganisms under optimum and continual supply of nutrients in an open system in industries.
CONTENTS
1. Overview and Key Difference
2. What is a Batch Culture
3. What is a Continuous Culture
4. Side by Side Comparison – Batch vs Continuous Culture
5. Summary
What is a Batch Culture?
Batch culture is a technique which grows microorganisms in a closed system where a limited amount of nutrients are supplied at the beginning. This is the commonest technique adopted in industries to make useful products using microorganisms such as bacteria and fungi. Microbe which grows in the fermenter ferments the nutrients. Fermentation is a breaking down process of carbohydrates into alcohols and acids by microorganisms under anoxic conditions. In batch culture technique, nutrients are provided at the beginning and the particular microorganism is inoculated into the fermenter. The fermenter is closed and the temperature and pH are maintained for the growth of microorganisms. Microorganism grows inside and utilizes the provided nutrients and other conditions. With time, nutrients become limited and the environmental conditions change within the fermenter. Hence, microbial growth shows distinct four stages such as lag phase, log phase, stationary phase, and death phase. At the end of the fermentation, the process is stopped and useful products are extracted and purified. The fermenter is washed and sterilized before using for another batch culture.
The specialty of the batch culture technique is, this is run under limited amounts of nutrients and for a certain time period. The fermenter setup is easy to make and handle. Environmental conditions inside the fermenter vary with time. However, required temperature, pH conditions, stirring, pressure, etc. are properly maintained to achieve successful product formation.
Batch culture technique is widely used for the purification of secondary metabolites such as antibiotics, pigments, etc. This technique is not suitable for the production of primary metabolites and products which are associated with growth.
Figure 01: Batch Culture
What is a Continuous Culture?
Continuous culture is another technique which grows useful microorganisms. It aims to maintain a continuously growing microbial culture at exponential phase. It can be achieved by supplying fresh nutrients continually, removing accumulated waste and products at the same rate and keeping other conditions at the optimum values. It is done inside a special chamber called chemostat as shown in figure 02. Fresh medium is added continuously from one end while metabolic products are continually extracted from the other end of the chemostat to keep the culture volume at a constant level.
Continuous culture is used in industries when it is required to extract useful primary metabolites such as amino acids, organic acids, etc. from the microorganisms. Primary metabolites are produced at the highest rate when the microorganisms are at their exponential phase. Hence continuous culture always aims to maintain the microbial biomass at the log phase. It is done by monitoring the process continually and controlling the system.
Figure 02: Continuous Culture in Chemostat
What is the difference between Batch and Continuous Culture?
Batch vs Continuous Culture |
|
| Batch culture technique is used to cultivate beneficial microorganisms under limited amounts of nutrients in a closed fermenter for a certain time period. Microbial growth inside the batch culture shows a typical microbial growth curve in which four distinct phases can be identified. | Continuous culture technique is used to grow beneficial microorganisms under optimum level of nutrients in an open system in which nutrients are added continually and waste and products are removed at the same rate to keep the growth at an exponential phase. |
| Nutrients | |
| Nutrients are supplied once before starting the fermentation process. | Nutrients are added many times (at starting and in between the process). |
| Type of System | |
| Batch culture is a closed system | Continuous culture is an open system. |
| Termination of Process | |
| The process of the batch culture is stopped after the product is formed. | The process is not stopped though the product is formed. Continuous removal of the product is done without stopping the process in continuous culture. |
| Environmental Conditions | |
| The environmental conditions inside the batch culture are not constant. | The environmental conditions inside the continuous culture are maintained at constant level. |
| Microbial Growth | |
| Microbial growth inside the batch culture follows lag, log and stationary phases. | Microbial growth is maintained at optimum level which is an exponential growth stage. |
| Turnover Rate | |
| Turnover rate is low since the nutrients and other conditions are limited inside. | Turnover rate is high since the optimum levels of nutrients and other conditions are maintained. |
| Fermenter Used | |
| A large size fermenter is used for batch cultures | A small size fermenter is used for continuous culture. |
| Use | |
| Batch culture fermentation is commonly used in industries | Continuous culture fermentation is less used in industries. |
| Culture Setup | |
| Batch culture setup is easy to make and run. | Continuous culture setup is not easy to make and run. |
| Contamination | |
| Contaminations are minimum in batch cultures | Contamination chance is high in continuous culture. |
| Controlling Methods | |
| Control methods are easy and quick. | Control methods are complicated and time-consuming. |
| Suitability | |
| Batch culture is more suitable for the production of secondary metabolites such as antibiotics. | Continuous culture is more suitable for the production of primary metabolites such as amino acids and organic acids. |
Summary – Batch vs Continuous Culture
Batch culture and continuous culture are two types of techniques employed to cultivate microorganisms in large scale for industrial and other purposes. In batch culture, microorganisms are provided with nutrients at the beginning and grown. When microbes utilize the available nutrients, nutrients become limited after certain time period. Microorganisms grow via lag, log, stationary and death phases. The fermentation process is carried out batch-wise in batch culture technique. After each and every batch, fermenter is cleaned and used freshly for the next batch. In continuous culture, microorganisms are provided with adequate levels of fresh nutrients continually to always maintain the microbes at log phase to extract primary metabolites of the microorganisms. The volume of the continuous culture is maintained at a constant value by adding fresh nutrients and removing products at the same rate without stopping the process. Batch culture is needed comparatively a large closed fermenter while continuous culture is needed a small open fermenter. This is the difference between batch and continuous culture.
References
1. Dionysis I. Foustoukos. “A Continuous Culture System for Assessing Microbial Activities in the Piezosphere.” Applied and Environmental Microbiology. N.p., 01 Oct. 2015. Web. 13 May 2017
2. Edward Robertson -. “Bacterial Growth : Batch vs Continuous.” Biogest. N.p., n.d. Web. 13 May 2017. <http://www.baccelerator.co.uk/batch.asp>.
Image Courtesy:
1. “Chemostat Vessel Diagram” By CGraham2332 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “The Small Fermenting Tanks” by Glyn Baker (CC BY-SA 2.0) via Geograph.UK