Microbes in Human Welfare - Notes | Class 12 | Part 1: Microbes in Household and Industrial Products


Several microbes such as bacteria, viruses, fungi etc. are useful to man in many ways. Some of them are given below:


·  Lactobacillus or Lactic acid bacteria (LAB):

-   It converts milk to curd by producing acids that coagulate and partially digest the milk proteins.

-   Fresh milk can be converted to curd by adding some curd containing LAB. It also increases vitamin B12 in curd.

-   In stomach, LAB helps to check pathogens.

·  Bacterial fermentation (anaerobic respiration) in dough is used to make foods such as dosa, idli etc. The puffed-up appearance of dough is due to the production of CO2.

·  Baker’s Yeast (Saccharomyces cerevisiae): It is used to make bread by fermenting dough.

·  Toddy is made by fermenting sap from palms.

·  Microbes are used to ferment fish, soya bean & bamboo-shoots and to produce cheeses.

·  Swiss cheese has large holes due to production of CO2 by Propionibacterium sharmanii (a bacterium).

  Roquefort cheese is ripened by growing a fungus (Penicillium roqueforti) on them.


Production of beverages, antibiotics etc. on an industrial scale, requires growing microbes in very large vessels (fermentors).

Fermented beverages

-    Saccharomyces cerevisiae (Brewer’s yeast) is used in the production of beverages by fermenting malted cereals and fruit juices to produce ethanol.

-    Wine & Beer are produced without distillation.

-    Whisky, Brandy, Rum, Gin, Arrack etc. are produced by distillation of fermented broth.


-    Chemical substances produced by some microbes and can kill or retard the growth of pathogens.

-    They are used to treat plague, whooping cough, diphtheria, leprosy etc.

-    Penicillin: First antibiotic discovered by Alexander Fleming. He observed that Staphylococci could not grow around a mould (Penicillium notatum) growing in unwashed culture plates. He extracted penicillin from it.

-    Earnest Chain and Howard Florey established its full potential as an effective antibiotic.

-    Fleming, Chain & Florey were awarded Nobel Prize (1945).

Chemicals, enzymes & other bioactive molecules

1.    Organic acids: Acid producer microbes include

Aspergillus niger (a fungus)                :    Citric acid

Acetobacter aceti (a bacterium)           :    Acetic acid

Clostridium butylicum (a bacterium)     :    Butyric acid

Lactobacillus (a bacterium)                 :    Lactic acid

2.    Alcohol: Yeast (S. cerevisiae) is used to produce ethanol.

3.    Enzymes:

·   Lipases: Used in detergent formulations. Help to remove oily stains from the laundry.

·   Pectinases & Proteases: To clarify bottled juices.

·   Streptokinase: Produced by Streptococcus. Used as a ‘clot buster’ to remove clots from the blood vessels of patients who have myocardial infarction.

4.    Cyclosporine A: Produced by Trichoderma polysporum (fungus). Used as an immunosuppressive agent in organ transplant patients.

5.    Statins: Produced by Monascus purpureus (a yeast). Used as blood-cholesterol lowering agents. It inhibits the enzymes responsible for synthesis of cholesterol.


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