Microbes as Industrial Chemists

Beverages and antibiotics are not the only things industry gets from microbes. On a commercial scale, microbes are grown to manufacture a range of ordinary but valuable chemicals — organic acids, alcohols and enzymes — that go into food, cleaning products and medicines. The idea is simple: a microbe that naturally produces some useful substance during its metabolism is grown in bulk, and the substance is harvested.

What makes this topic worth memorising is the precise pairings. For the examinations you are expected to know exactly which microbe yields which product, and whether that microbe is a fungus or a bacterium. So it helps to sort them into acid producers, alcohol producers, enzyme sources and the special bioactive molecules used in medicine.

Organic Acids and Alcohol

Several everyday organic acids are made industrially by microbes. Learn these pairings carefully, because they are asked frequently:

  • Aspergillus niger, a fungus, produces citric acid.
  • Acetobacter aceti, a bacterium, produces acetic acid.
  • Clostridium butylicum, a bacterium, produces butyric acid.
  • Lactobacillus, a bacterium, produces lactic acid.

Notice that only the citric-acid producer is a fungus; the other three acid producers are bacteria. For alcohol, the familiar yeast steps in again: Yeast, Saccharomyces cerevisiae, is used for the commercial production of ethanol. This is the same organism you met as baker's and brewer's yeast, now put to work industrially.

Enzymes That Do Household Jobs

Microbes are also grown to produce enzymes, and two everyday applications make this concrete.

Lipases are used in detergent formulations. Because lipases break down fats, they help remove oily stains from laundry — which is why enzyme-based detergents clean greasy marks that plain soap struggles with.

The second example you have almost certainly noticed yourself: bottled fruit juices bought from the market are clearer than the ones made at home. That clarity is not an accident. The bottled juices are treated with pectinases and proteases, enzymes that break down the pulp and suspended proteins so the juice turns out clear rather than cloudy.

Life-Saving Bioactive Molecules

Some of the most valuable microbial products are bioactive molecules used in medicine. Three of them are essential to remember, along with their exact sources and functions.

Streptokinase is produced by the bacterium Streptococcus and then modified by genetic engineering. It is used as a 'clot buster' — it dissolves and removes clots from the blood vessels of patients who have had a myocardial infarction, that is, a heart attack.

Cyclosporin A is an immunosuppressive agent given to organ-transplant patients to stop their bodies rejecting the new organ. It is produced by the fungus Trichoderma polysporum.

Statins, produced by the yeast Monascus purpureus, are blood-cholesterol lowering agents. They work by competitively inhibiting the enzyme responsible for the synthesis of cholesterol, so less cholesterol is made in the body.

Quick Recap

  • Microbes are grown commercially to make organic acids, alcohols and enzymes.
  • Acid producers: Aspergillus niger (fungus) makes citric acid; Acetobacter aceti (bacterium) makes acetic acid; Clostridium butylicum (bacterium) makes butyric acid; Lactobacillus (bacterium) makes lactic acid.
  • Alcohol: yeast Saccharomyces cerevisiae produces ethanol commercially.
  • Enzymes: lipases remove oily stains in detergents; pectinases and proteases clarify bottled fruit juices.
  • Bioactive molecules: streptokinase from Streptococcus (genetically modified) is a clot buster after heart attacks; cyclosporin A from Trichoderma polysporum is an immunosuppressant for transplants; statins from Monascus purpureus lower blood cholesterol by inhibiting the cholesterol-synthesising enzyme.

Solved Examples — Section 5

Q1. Name the microbe and its product for citric acid, and state whether it is a fungus or a bacterium.

Answer: Citric acid is produced by Aspergillus niger, which is a fungus.

Q2. Which yeast is used for the commercial production of ethanol?

Answer: Saccharomyces cerevisiae.

Q3. Why are bottled fruit juices clearer than those made at home?

Answer: The bottled juices are clarified using the enzymes pectinases and proteases, which break down pulp and suspended proteins, making the juice clear.

Q4. What is streptokinase used for, and from which microbe is it obtained?

Answer: Streptokinase, produced by the bacterium Streptococcus and modified by genetic engineering, is used as a 'clot buster' to remove clots from the blood vessels of patients who have had a heart attack (myocardial infarction).

Q5. Name the source and role of cyclosporin A.

Answer: Cyclosporin A is produced by the fungus Trichoderma polysporum and is used as an immunosuppressive agent in organ-transplant patients.

Q6. How do statins lower blood cholesterol, and which microbe produces them?

Answer: Statins, produced by the yeast Monascus purpureus, act by competitively inhibiting the enzyme responsible for the synthesis of cholesterol, thereby lowering blood cholesterol.