Cambridge O Level Biology · Syllabus 5090 · Biotechnology and Genetic Modification
Fermenter
What is Fermenter?
A large vessel, usually of stainless steel, in which microorganisms are grown on a commercial scale under controlled conditions so that a useful product can be collected. A fermenter allows temperature, pH, oxygen supply, nutrient supply and waste products all to be controlled at once. Typical features include a cooling jacket to remove the heat released by respiration, temperature and pH probes, inlets for nutrients and for acid or alkali, a sterile air inlet through a sparger for aerobic processes, a motor-driven impeller to distribute heat, nutrients and oxygen, an inoculation port, a sampling port, an exhaust outlet and a product outlet. Whether air is supplied depends on the organism and the product: an anaerobic process limits or excludes it.
This definition is part of the Biotechnology and Genetic Modification chapter in Cambridge O Level Biology.
Fermenter in context
Biotechnology is the use of living organisms, cells or enzymes to make useful products. Yeast respires anaerobically, converting glucose to ethanol and carbon dioxide: the carbon dioxide raises bread dough, and the ethanol is the product collected in ethanol manufacture. Bacteria are chosen for industrial production because they reproduce rapidly, can make complex molecules, contain plasmids that can receive selected genes, and raise fewer ethical concerns than using animals. They are grown in fermenters, in which temperature, pH, oxygen, nutrient supply and waste products are all controlled. Isolated enzymes do industrial jobs of their own — proteases and lipases in biological washing powders, pectinase in fruit juice, lactase in lactose-free milk. Genetic modification is changing an organism's genetic material by removing, changing or inserting individual genes; inserting the human insulin gene into bacterial DNA lets bacteria make human insulin, and inserting genes into crops can give herbicide resistance, insect-pest resistance or increased vitamin content — each with benefits and risks that have to be weighed rather than declared.
Common mistakes with Fermenter
- “All industrial fermentation is anaerobic.” Why wrong Many fermenters have a sterile air inlet precisely because the organisms inside them respire aerobically. If oxygen were never wanted, the inlet would not exist.
- “The modified bacteria are injected into the patient.” Why wrong The purified protein is what is used. The bacteria stay in the fermenter, and separating the insulin from them is step 7 for exactly this reason.
- “The insulin comes out of the fermenter ready to use.” Why wrong It is mixed with bacteria, culture medium and everything else in the vessel. It must be separated and purified, and its quality checked, before it is prepared for medical use.
- “All fermentation is anaerobic.” Why wrong True of yeast fermentation, but an industrial fermenter is a vessel, not a process, and many processes run in one are aerobic — which is why the sterile air inlet exists. Say instead In yeast, fermentation is anaerobic respiration. In a fermenter, whether oxygen is supplied depends on the organism and the product.
- “Fermenters should be kept as hot as possible.” Why wrong Above the optimum, enzymes denature and cells die. And a large fermenter is already overheating from the heat its own microorganisms release. Say instead The culture is held near a suitable temperature, and cold water in the cooling jacket removes the excess heat produced by respiration.
- “The fermenter is heated to make the reactions go faster.” Why wrong The control problem in a running fermenter is removing heat, not adding it. Say instead Respiration releases thermal energy, so the culture is cooled to keep it near the optimum for its enzymes.
- Fermenters are heated as hot as possible.
Examiner tips on Fermenter
- Two words worth spelling carefully. Write fermenter, not fermentor, and write plasmid, not plastid — a plastid is a plant organelle and belongs in a different chapter entirely.
Questions students ask about Fermenter
What is biotechnology?
Biotechnology is the use of living organisms, cells or enzymes to make useful products or to carry out useful processes. It includes using yeast to make bread and ethanol, growing bacteria in industrial fermenters, and using isolated enzymes such as proteases, pectinase and lactase. Genetic modification is one technique used within biotechnology, not another name for it.
What conditions are controlled in an industrial fermenter?
Temperature, pH, oxygen supply, nutrient supply and waste products. Temperature is controlled because respiration releases heat that would otherwise denature the enzymes; pH because metabolism releases acidic or alkaline waste and enzymes work best in a narrow range; oxygen according to whether the process is aerobic or anaerobic; nutrients because the culture needs carbon, nitrogen, minerals and other raw materials; and wastes because they can be toxic and slow production.
Why is a fermenter cooled rather than heated?
A large fermenter contains an enormous number of microorganisms, all respiring and all releasing thermal energy. Together they would raise the temperature above the optimum, denaturing enzymes and killing cells. Cold water is circulated through a cooling jacket to carry the excess heat away.
Is industrial fermentation always anaerobic?
No. In yeast, fermentation means anaerobic respiration, but an industrial fermenter is a vessel rather than a single process, and many processes run in one are aerobic and need sterile air supplied through a sparger. Whether oxygen is supplied depends on the organism and the product wanted.
What happens if a fermenter becomes contaminated?
Unwanted microorganisms compete with the chosen organism for the nutrients supplied, so fewer of the chosen cells grow and the yield falls. The contaminants' own waste products may alter or spoil the product, and some contaminants create a safety risk, so the batch may have to be discarded.
How is human insulin made using bacteria?
The human gene controlling insulin production is identified and cut out of human DNA. A bacterial plasmid is cut open and the gene is joined into it, forming a recombinant plasmid, which is introduced into bacteria. The modified bacteria are cultured in a fermenter under controlled conditions and express the gene, producing human insulin, which is then separated from the culture and purified for medical use.
Are the modified bacteria given to patients?
No. The bacteria remain in the fermenter. The insulin they produce is separated from the culture and purified, and it is the purified protein that is prepared for medical use.