Microorganisms in Biotechnology

Biotechnology is the use of living organisms, cells or cell components to produce useful products. Microorganisms — bacteria, yeasts and fungi — are the workhorses of biotechnology because of their rapid growth, genetic flexibility, and ability to synthesise complex molecules in large quantities. OCR A-Level Biology A specification 6.2.1 (d)–(e) requires you to know the roles of microorganisms in food production, brewing and pharmaceuticals, and to evaluate their advantages and disadvantages.

Key Definitions:

• Biotechnology — the industrial use of living organisms or their products.
• Fermentation — anaerobic metabolism by yeast or bacteria producing useful products (ethanol, lactic acid, CO₂).
• Primary metabolite — a substance produced by a microorganism during normal growth (e.g. ethanol).
• Secondary metabolite — a substance produced after the main growth phase, often under stress (e.g. penicillin).
• Single-cell protein (SCP) — protein produced by microorganisms for human or animal food.

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Why Use Microorganisms?

Microorganisms have several advantages over plants and animals for producing useful substances:

• Rapid growth — bacteria can double every 20–30 minutes; animals take years.
• Cheap substrates — many microorganisms grow on waste materials (molasses, whey, cellulose).
• Controlled conditions — temperature, pH and nutrients can be precisely regulated in a fermenter.
• No ethical issues compared to animal products.
• Easy genetic manipulation — GM bacteria can produce human proteins (Lesson 2).
• High yields — vast quantities of product from small fermenters.
• No seasonal limitations — year-round production independent of climate.
• Can be used in developing countries — no refrigeration needed for fermented foods.

Disadvantages include the need for aseptic technique to prevent contamination, careful downstream processing to purify products, and sometimes consumer suspicion of microbial origin.

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Food from Microorganisms

Brewing and Wine-Making

Humans have fermented beer and wine for over 10,000 years. Both rely on yeast (Saccharomyces cerevisiae for beer and most wine; S. ellipsoideus for traditional wine) converting sugar to ethanol and carbon dioxide anaerobically:

$\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\text{C}_2\text{H}_5\text{OH} + 2\text{CO}_2$C6​H12​O6​→2C2​H5​OH+2CO2​

• Beer is made from malted barley. Malting germinates the barley, activating amylase which hydrolyses starch to maltose. The resulting "wort" is boiled with hops (for bitterness and preservation), cooled, and fermented with yeast for about a week. Lager uses bottom-fermenting yeast at low temperature; ale uses top-fermenting yeast at higher temperature.
• Wine is made from grape juice, which already contains sugar and wild yeast on the skins. Modern wine uses cultured yeast strains for consistency. Fermentation takes 1–2 weeks, followed by months to years of maturation.
• Spirits (whisky, gin, vodka) are produced by distillation of fermented liquids, concentrating the ethanol well above 12–15% (the tolerance limit of yeast).

Baking

Bread dough contains yeast, which ferments the sugars in flour. The CO₂ produced becomes trapped by the gluten network, making the dough rise. The ethanol evaporates during baking. Fast-action dried yeast is a selected strain of S. cerevisiae.

Cheese

Cheese-making uses lactic acid bacteria (Lactobacillus, Lactococcus, Streptococcus) to convert lactose in milk to lactic acid, lowering the pH. This causes the milk protein casein to coagulate. Rennet (containing chymosin — now usually produced by GM microorganisms) accelerates coagulation. The curds are separated from the whey, pressed and aged. Specific cultures give characteristic cheese flavours: Penicillium roqueforti (Roquefort, Stilton), P. camemberti (Camembert, Brie), Propionibacterium (Swiss cheese and its holes from CO₂).

Yoghurt

Yoghurt is made by adding Lactobacillus bulgaricus and Streptococcus thermophilus to warm milk (40–45 °C). The bacteria ferment lactose to lactic acid, which curdles the milk protein and gives the characteristic tart flavour. Probiotic yoghurts add Lactobacillus acidophilus and Bifidobacterium for claimed gut-health benefits.

Vinegar

Acetobacter bacteria oxidise ethanol (from wine or cider) to acetic acid, producing vinegar.

Soy Sauce and Miso

Traditional Japanese foods are fermented with Aspergillus oryzae (a mould), followed by lactic acid bacteria and yeast, over months.

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Single-Cell Protein: Mycoprotein (Quorn)

Mycoprotein (trade name Quorn) is a meat substitute produced by fermenting the fungus Fusarium venenatum in huge continuous fermenters at Billingham, County Durham. The fungus is grown on glucose syrup (typically from wheat starch) with added ammonia (nitrogen source) and mineral salts at 28–30 °C and pH 6.