21.2 - Industrial Fermentation

Culturing microorganisms industrially

• Many useful substances are made by growing microorganisms (bacteria and fungi) on a large industrial scale.
• The microorganisms are grown inside large vessels called fermenters.
• A fermenter is filled with a liquid culture medium - a nutrient-rich liquid in which the microorganisms can grow and reproduce in huge numbers.
• As they grow, the microorganisms make the wanted product.

Products made this way

• Penicillin - An antibiotic, produced by growing the fungus Penicillium
• Human insulin - Used to treat diabetes, produced by growing genetically modified bacteria that carry the human insulin gene
• Mycoprotein - A protein-rich food used as a meat substitute, produced by growing the fungus Fusarium

Getting the maximum yield

• The conditions inside the fermenter are monitored and kept at the optimum (best) levels for the microorganisms' growth, so the yield of product is as large as possible.
• Once enough product has built up, the culture medium is drained off and the product is separated out and purified.

Fermenter design and the conditions controlled

• Microorganisms are grown on a large scale inside an industrial fermenter - a large vessel filled with a liquid culture medium.
• Conditions inside are monitored and held at the optimum levels for growth. The more the microorganisms grow, the greater the yield of product.

Conditions controlled inside the fermenter

• Nutrients - The liquid culture medium supplies all the nutrients the microorganisms need to grow and reproduce.
• Temperature - Monitored and kept at the optimum. The microorganisms release heat as they respire, so a water-cooled jacket around the vessel removes excess heat and stops it getting hot enough to denature the enzymes.
• pH - A pH probe monitors the pH, which is kept at the optimum (by adding acid or alkali) so the microorganisms' enzymes work as efficiently as possible.
• Oxygen - If the microorganisms respire aerobically, sterile air is pumped in to supply oxygen, so they can always release the energy needed for growth.
• Agitation - Paddles stir and circulate the medium, keeping the microorganisms in contact with fresh nutrients and keeping temperature and pH even throughout.
• Sterility - The vessel is sterilised between uses with superheated steam to kill unwanted microbes. These aseptic conditions stop other organisms competing with the culture and stop the product being contaminated.
• Waste removal - Waste gases such as carbon dioxide are let out through an exhaust so they don't build up and spoil the growing conditions.

Harvesting the product

1. When the culture is fully grown, the medium is drained off and filtered.
2. The product is then extracted and purified.

Producing human insulin in a fermenter

Human insulin can be produced by genetically modified bacteria - bacteria that carry the human insulin gene, so they make human insulin as they grow.

How it's produced

1. The genetically modified bacteria are grown in huge numbers inside a fermenter, under controlled conditions that keep them growing and reproducing quickly.
2. As they grow, the bacteria make insulin.
3. Once a large amount has been produced, the insulin is harvested from the culture.
4. It is then purified to remove the bacteria and other unwanted material.

What the insulin is used for

• The purified human insulin is used to treat people with diabetes.
• These include people with Type 1 diabetes, whose pancreas does not make enough insulin.