In recent years, development in fermentation technology and microbial biotechnology has allowed efficient use of microorganisms for the production of important commodities like cheese, bread, beer, tea, coffee, chocolate, antibiotics, and various other primary and secondary metabolites. These products are a result of the ability of the microorganisms to ferment specific metabolites into the desired product.
To obtain the desired product, and promote the growth of microorganisms, a controlled environment must be used, providing conducive conditions under which optimal growth can be obtained. This includes a controlled pH, optimum temperature, air inflow, culture medium flow rates, agitation speed, etc. Such production is done in a large vessel or tank, called a bioreactor, which allows mass quantities of a product to be obtained, by growing microorganisms in large volumes. Microorganisms allowed to grow in the bioreactor under favourable conditions will produce the desired product, which can be purified. In essence, each of the millions of cells per unit area used in a bioreactor is a micro-bioreactor in its own right.
A typical bioreactor has the following parts- the main vessel or tank, a cooling and heating system, a well-developed aeration system, feed ports, a foam control system, and a waste port.
Batch Reactors − It is a simple, closed system, hence once inoculated, the tank receives no more input and no output is allowed. Eventually, waste materials start to pile up, while the nutrients and oxygen levels decline.
Continuous Stirred Tank Bioreactors (CSTRs) − such a bioreactor involves continuous input and output. Hence, the culture medium containing required nutrients and reactants is continuously fed into the bioreactor, and the products of the bio-reaction are simultaneously extracted from the tank. Hence, continuous chemical processing is carried out in such tanks.
Airlift Bioreactors − such bioreactors are especially used when working with aerobic cell cultures, or when the final product to be obtained is in gaseous form. Gas is used to agitate the contents of the vessel. The gas fed into the vessel is also used to introduce new materials into the vessel, or remove the metabolic molecules that have been produced by the microbial cells.
Fixed-bed bioreactors − such bioreactors involve the immobilisation of the reacting cells to a surface of packed solid particles. The solid particles may be porous or non-porous.
Photobioreactors − Such bioreactors are different from the others in that they are made of transparent materials like glass or plastic. These tube-shaped or flat panel bioreactors are illuminated either by the sun or by artificial light, supporting the growth of photosynthetic microbes
Bioprocess refers to employing living microbial cells for the production of desired products. The success of a bioprocess depends on the ability of the microorganism to grow in the physicochemical environment provided to it.
A typical bioprocess comprises three steps- the three P’s, which are −
Preparation − also called “upstream processing”, this step involves −
Preparation of all materials and equipment that are to be used in the production process. It also involves equipment sterilization and air purification
Identification and development of desirable strains. Strains are also improved using different methods
Optimization of conditions suitable for optimal growth of culture and obtaining desired products
Production − this is the main stage, where bioprocessing occurs. The cells react under ambient conditions to form the desired metabolic product. The cells are continuously dividing and metabolising during this stage.
Purification − aka “downstream processing”/ product recovery, this step involves the removal of impurities, separation of the desired product from the rest of the medium, and the purification of the obtained product.
Microbial biotechnology involves the application of principles of biotechnology to microorganisms, for the desired processing of microbes to allow the production of required products. These microbes may be naturally isolated strains, mutant strains from lab cultures, or they may be recombinant strains, created via genetic engineering.
The steps involved in obtaining foreign gene product are −
Isolating the gene of interest
Identifying a suitable vector for carrying the gene of interest. The gene is ligated into the vector using ligase. This results in “recombinant DNA”
Transfer of the r-DNA into a suitable host such as a bacterial cell. The cell now carries a “foreign gene”
Selecting recombinant cells
Expression of desired protein/ metabolite by recombinant cells
Large-scale production of the desired product by culturing in large bioreactors
Cell separation and product recovery
Bioreactors are advantageous equipment that allows a controlled growth of microorganisms to obtain the desired product. It facilitates optimal growth conditions by allowing control of factors such as pH, nutrient concentration, oxygen concentration, temperature, etc. Since almost everything is automated, it helps in cutting labour costs as well.
The production of secondary metabolites such as penicillin, cyclosporin-A, lovastatin, etc.
The production of fermented dairy products like cheese, buttermilk, yoghurt, etc
The production of citric acid, lactic acid, acetic acid, and other organic acids
Production of important enzymes like laccase, xylanase, lipase, etc
Sometimes, bioreactors are used for the production of microbial cells and not their products. This is seen in the case of single-cell proteins, yeast production, production of Lactobacillus, etc.
Bioreactors are also used to culture mammalian cells
Photobioreactors are used in wastewater treatment, growing algae and cyanobacteria to obtain biofuels, bioplastics, nutraceuticals, etc.
Bioreactors are large vessels or tanks in which microbial cells are cultured in a controlled environment to obtain their useful products
Different types includes fed-batch bioreactor, continuous stirred tank reactor, fixed-bed bioreactor, photobioreactors, etc.
Bioreactor processes are instrumental in the production of antibiotics, products such as cheeses, beers, vinegar, etc., organic acids, and other important metabolites, wastewater treatment and production of microbially- obtained biofuels and bioplastics, among several other applications
A typical bioprocess involves- preparation, production and purification
Cells used may be genetically modified by introducing a foreign gene into them, to produce the desired protein, or, to increase the product yield
Q1. What type of material is the ideal bioreactor made of?
Ans. Bioreactors should be made of non-corrosive material, that can tolerate steam sterilization, high pressure and pH changes.
Q2. What kind of microorganisms are grown in a photobioreactor?
Ans. Photobioreactors are used for photosynthetic cyanobacterial cultures or microalgal cultures
Q3. What are the bioplastics produced by microorganisms?
Ans. Polyhydroxyalkanoates (PHAs) such as Polyhydroxybutyrate (PHB) are plastics produced by microbes
Q4. What are the strain improvement methods employed in a bioprocess?
Ans. Protoplast fusion, genome shuffling, mutation, recombination, etc. are used to improve strains in a bioprocess.
Q5. How are primary metabolites different from secondary metabolites?
Ans. Primary metabolites are produced during the growth phase and are necessary for the growth and reproduction of the organism. Secondary metabolites are derived from primary metabolites. These substances have an ecological function and don’t affect the growth and reproductive abilities of an organism.
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