Cell culture is the removal of cells from an animal or plant and their subsequent growth in a favourable artificial environment provided with a proper medium and sterile environment. The goal of cell culture systems is to develop and investigate cells in a three-dimensional environment in tissues by providing appropriate in vitro conditions.
Why would we need to mass-produce organisms? These microbes can be compared to miniature protein factories, with each cell producing a specific amount of the desired product.

Small amounts of these cells can be grown in beakers and flasks by scientists in the lab, but what if we needed a lot? Many pharmaceutical medications, for example, are constructed up of recombinant proteins, which would require hundreds of litres of cell culture. The solution is to build a factory that promotes the expansion of smaller factories! A bioreactor is a device that permits recombinant cells to grow at a large scale and create enormous amounts of recombinant proteins. Let us study the Growth and Maintenance of Cell Culture and the Biochemical Engineering Process. 

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Obtaining the Foreign Gene Product 

1. The first step to obtaining a foreign gene product is identifying and isolating the gene of interest.
2. Adding or ligating the gene of interest into suitable vector results a complete recombinant DNA molecule. 
3. Transfer of this recombinant DNA molecule into the suitable host cell. Selection of recombinant and non-recombinant cells. 
4. Expression of the gene of interest by culturing recombinant cells under suitable conditions. 
5. The culturing of cells in bioreactors for large-scale production of the desired product.
6. If any protein-encoding gene is expressed in a heterologous host, is called a recombinant protein.
7. The recombinant cells can be multiplied on a large scale using a continuous culture system. 
8. Here the cells are cultured in a large vessel, and the medium is refreshed on a regular interval to maintain the optimum conditions. 
9. This helps to culture a large mass of the desired protein. This was achieved by the development of bioreactors.

Bioreactor

A bioreactor is a type of fermentation vessel used to produce various chemicals and biological reactions. It is a closed container with adequate arrangement for aeration, agitation, temperature and pH control, and drain or overflow vent to remove the waste biomass of cultured microorganisms along with their products.

Fig: Stirred Tank Bioreactor

1. A bioreactor is a large volume vessel of approximately (100 – 1000 L) in which, raw materials are biologically converted into specific products, individual enzymes, etc.
2. The bioreactor is a large vessel where the different cells such as human or plant or animal cells are used to culture new biological products. 
3. It provides optimum conditions like temperature, pH, substrate, oxygen, etc, required culturing of desired products. 
4. The cells can also be multiplied in a continuous culture system. In this, the used medium is drained out from one side, while a fresh medium is added from the other side to maintain the cells in their physiologically most active log/exponential phase.
5. This type of culturing method produces larger biomass leading to higher yields of the desired protein.
   a. The components of bioreactors are
   b. An agitator system
   c. An oxygen delivery system
   d. A foam control system
   e. A temperature control system
   f. pH control system
   g. A sampling port to withdraw culture periodically
6. The most used bioreactors are of stirring type. Stirring type bioreactors are further of two types, i.e., simple and sparged.
7. A simply stirred tank bioreactor is usually cylindrical or with a curved base to facilitate even mixing of reactors contents.
8. The sparged stirred tank bioreactors also facilitate mixing components and ensure oxygen availability throughout the bioreactor. Alternatively, the air is bubbled through the reactor.

Types of Bioreactor

The fermentor (bioreactor) types used extensively in industries are

1. Continuous stirred tank fermentor

1. A continuous stirred tank bioreactor is made of a cylindrical vessel with a central shaft controlled by a motor that supports one or more agitators (impellers). 
2. The sparger, in combination with impellers (agitators), allows for improved gas distribution throughout the vessel.
3. A stirred tank bioreactor can be operated continuously in the fermentor, temperature control is effortless, construction is cheap, easy to operate, resulting in low labour cost, and easy to clean.
4. It is the most common type of bioreactor used in industry.

2. Airlift fermentor

1. The airlift reactor is generally used for gas-liquid or gas-liquid-solid contact devices. It is also known as a tower reactor. 
2. A bioreactor using an airlift system divides the fluid volume into two zones to improve circulation, oxygen transfer, and equalize forces in the reactor
3. In a two-zone system, only one zone is sparged with gas. The zone where the gas is sparged is the riser; the zone in which it is not sparged in the downcomer.
4. Airlift bioreactors are used for aerobic bioprocessing technology so that they can provide a controlled liquid flow in a recycling system using pumps. 
5. This equipment has several advantages such as its simplicity of design because it doesn’t contain any moving parts or agitators, its easy sterilization, its low energy requirements, and its low cost.

3. Bubble column fermentor

1. The bubble column fermentor consists of a cylindrical vessel equipped with a gas sparger that pushes gas bubbles into a liquid phase or a liquid-solid suspension.
2. The base of the column air or gas is introduced via perforated pipes or plates, or metal micro porous sparger.
3. The rheological properties of the fluid and the gas flow rate have a significant influence on the mixing of O2 and other performance factors.
4. To improve mass transfer and modify the basic design of the vessel, internal devices such as horizontal perforated plates, vertical baffles, and corrugated sheet packings placed are in the vessel.
5. These reactors are simple in construction, easy maintenance, and have a low operating cost.
6. Bubble columns reactors are used in biochemical processes such as fermentation and biological wastewater treatment. It is also used in many chemical, petrochemical, and biochemical industries.

Applications of Bioreactor

Some important applications of the bioreactor are:

1. Ethanol fermentation is done by saccharomyces cerevisiae in the bioreactor.
2. Organic Acids e.g., acetic acid and butyric acid are formed in the bioreactor by the Eubacterium limosum.
3. Thienamycine is an antibiotic also produced in bioreactors.
4. Glucomylase is produced by Auerobasidium pullulans in a bioreactor.

Downstream Processing

1. Downstream processing is a sequential step in which, the isolation, purification, preservation of final products is done before it is marketed. 
2. In this stage, the final product is formulated with additives like preservatives, colours, etc, followed by clinical trials.
3. After completion of the biosynthetic phase, the product must be subjected to a series of processes before is ready for marketing as a finished product. 
4. The processes include
5. Separation and Purification of products, which are collectively called downstream processing. The product is then subjected to quality control testing and formulated with the addition of suitable preservatives. 
6. Downstream processing and quality control tests generally differ from product to product.

Summary

Recombinant DNA technology is the process that involves the introduction of a foreign piece of DNA into the genome which contains our genes of interest. This gene introduced is the recombinant gene and the technique is called recombinant DNA technology. Inserting the desired gene into the genome of the host is not as easy as it sounds. The aim is to obtain desirable protein. A bioreactor is a high-volume vessel (100-1000 L) in which, raw materials are biologically transformed into specialised products, enzymes, and other substances. The bioreactor is a huge vessel used to develop new biological products using various cells such as human, plant, or animal cells. It creates ideal circumstances for the culturing of desired goods, such as temperature, pH, substrate, oxygen, and so on.

FAQs

Q.1. What are bioreactors and their types?
Ans: There are three types of bioreactors:
1. Stirred-tank bioreactor
2. Simple stirred-tank bioreactor
3. Sparged stirred-tank bioreactor

Q.2. What is the use of bioreactors?
Ans: A bioreactor is a complex system designed to produce compounds and substances with the help of cells or whole organisms. These compounds are then used as finished products, such as beer or are treated in additional processing steps to get an isolated compound such as vaccines or proteins.

Q.3. What is downstream processing?
Ans: Downstream processing is the recovery and purification of biochemical products with proper treatment. It is a series of events that includes cell separation, filtration, product recovery, extraction of product and purification and then treatment of product by chemical, physical and biological means.

Q.4. What is a simple stirred-tank bioreactor?
Ans: The stirred tank bioreactor, which consists of a cylindrical vessel with a stirrer, is a basic and commonly used fermenter design. For millennia, the design has been utilised extensively in all microbial fermentation and has been the primary system for yeast fermentation in the brewing industry.

Q.5. What is a cell culture?
Ans: Cell culture is keeping the cells taken out of a source in an artificial environment alive. The goal of cell culture systems is to develop and investigate cells in a three-dimensional environment in tissues by providing appropriate in vitro conditions.

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