Biotechnology: Screening Procedures, Fermentation and the Production of Penicillin, Industrial Enzymes

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Screening Procedures

Micro-organisms are used in industry for a large number of processes. This is because they have simpler nutrient requirements, fast growth rates and can be genetically manipulated. Before using micro-organisms, they must be screened to find the most suitable for a particular process.

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For example, fungi can be grown with several bacteria to see if they have any antibiotic effect. Similarly, bacteria can be screened for protease production. Agar plates are treated with casein - a protein that makes it cloudy. If the bacteria produce protease, a clear area where the casein has been hydrolysed will form; the larger this area is, the higher the concentration of protease that has been produced.

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Screening bacteria for protease production.

Fermentation and the Production of Penicillin

For detail on the fermenter see fermentation.

There are two types of culturing techniques used to grow large amounts of micro-organism. Batch culturing has all substrates added together ar the start and the products harvested at the end. The cells are in the exponential growth for a smaller period and the amount of product is limited by the initial amount of substrate. This means batch culturing is less productive but contamination is less likely. Sometimes it is necessary to use batch culturing: bacteria or fungus will not produce antibiotic in the exponential phase because there isn't much competition.

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Another process is continuous culture where new substrate is continually added and product continually harvested. In this method the cells are maintained in the exponential growth phase. It makes a lot of product and once you have got the conditions right, is automatic. However, the fermenter can only be used for one product and contamination is more likely.

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batch and continuous culturing techniques

The products of fermentation are not usually purely what you want (notable exceptions are in food production: beer, yogurt etc). So downstream processing is carried out to extract purified product, as is the case in Penicillin production (stages 3, 4 & 5 in the diagram below).

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The antibiotic Penicillin is obtained from a strain of the mould Penicillium chrysogenum. It is fermented in a batch culture as if the P. chrysogenum is kept in the exponential phase it uses the energy to grow rather than make Penicillin.

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The main stages of Penicillin production are:

the main stages in penicillin production

Industrial Enzymes

Micro-organisms can be used to produce enzymes that are useful in certain industrial applications. A more efficient method of using them is to isolate an enzyme and use it by itself. This is better because higher concentrations of enzyme can be obtained and only one reaction is taking place - whereas using whole micro-organisms would have numerous enzyme reactions and more products to process.

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A further problem is encountered in that enzymes are expensive to produce. This is solved by reusing the enzyme, this is made possible by immobilising the enzymes, this way they do not contaminate the end products are can be reused.

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Some methods of immobilising an enzyme are:

Method How it works Illustration
Bonding with cross-linking agent. Enzymes are linked to each other by chemical bonds. They may all be joined by amino acids for instance.
cross-linking enzymes
Entrapment inside a gel. Enzyme is trapped in an inert 'matrix' such as alginate or collagen, and cannot be washed out. Substrates and products though, may diffuse in and out of the matrix. This type of enzyme takes the form of small beads.
entrapment of enzymes inside a gel
Binding to an adsorbing agent. A support matrix (glass beads or carbon) has enzymes attached to it by weak forces (a bit like magnetism). The adsorption may alter the enzymes shape, though, and the force might be too weak to hold the enzymes in place very strongly.
adsorbing an enzyme

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Categories : Micro

Recent edits by: Jamie (ScienceAid Editor)

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