Introduction to Microbiology Class 10 Notes, Questions | SSC

This chapter introduces applied and industrial microbiology, the branches that put microbes to work for society. It explains how bacteria, yeast and fungi are used to make yoghurt, cheese, butter, probiotics, bread, vinegar, beverages, organic acids, enzymes and antibiotics. It then covers microbial fuels, waste and sewage management, clean technology for oil spills, plastic and acid pollution, and the use of microbes in farming as inoculants and bioinsecticides.

Summary

Applied microbiology studies enzymes and proteins of prokaryotic and eukaryotic microbes, applied genetics and molecular biology, and uses this knowledge to produce food, medicines and other products on a large scale. Industrial microbiology deals with the commercial use of microbes: fermentation-based production of bread, cheese, wine, enzymes, nutrients, medicines and chemical raw materials, and the use of microbes in garbage management and pollution control.

Milk is converted into cheese, butter, cream, kefir and yoghurt to preserve it. Most milk products use bacteria; only cheese involves fungi. Milk is first pasteurized to kill unwanted microbes and then fermented by lactobacilli, which turn lactose into lactic acid; the acid coagulates milk proteins, and flavour compounds such as diacetyl (butter flavour) are formed. For industrial yoghurt, Streptococcus thermophilus and Lactobacillus delbrueckii are added in a 1:1 ratio to warm milk; lactic acid from Streptococcus gels the proteins, and acetaldehyde-like compounds from lactobacilli give the taste. Butter is made as sweet cream and cultured types, and microbes are used for the cultured type.

For cheese, tested milk is mixed with Lactobacillus lactis, Lactobacillus cremoris and Streptococcus thermophilus, whey is removed, and the curd is cut, washed, salted, flavoured, pressed and ripened. Rennet from the alimentary canal of cattle was used earlier, but fungal protease is now used to make vegetarian cheese. Fresh cheese (cottage, cream, mozzarella) is soft, cheddar forms after 3 to 12 months and very hard parmesan after 12 to 18 months of ripening. Because bacteria can be attacked by viruses, strict hygiene, virus-resistant and mutant strains are used.

Probiotics are milk products with active bacteria such as Lactobacillus, Acidophilus, Lactobacillus casei and Bifidobacterium bifidum. They increase helpful intestinal microbes, reduce harmful ones like Clostridium, improve resistance, reactivate useful microbes made inactive by antibiotics, and are used to treat diarrhoea and in poultry. Bread dough rises because baker's yeast Saccharomyces cerevisiae ferments sugar into carbon dioxide and ethanol; the gas makes bread spongy, and the yeast's own carbohydrates, fats, proteins, vitamins and minerals make it nutritious.

Vinegar, chemically about 4% acetic acid, is made by first fermenting fruit juice, syrup, molasses or starch into ethanol with yeast, then converting ethanol into acetic acid with Acetobacter and Gluconobacter; it is then separated, bleached with potassium ferrocyanide, pasteurized and treated with a little SO2. Soya sauce is made by fermenting wheat or rice flour and soyabean with the fungus Aspergillus oryzae. Microbes also help in making coffee, cocoa, wine and cider, and in producing organic acids such as glutamic acid (for monosodium glutamate), citric acid, gluconic acid, lactic acid and itaconic acid, as well as colours, flavours, sweeteners and xanthan gum (from Xanthomonas).

Microbial enzymes are replacing chemical catalysts because they work at low temperature, pH and pressure, save energy, give specific products without unwanted by-products, can be reused and are eco-friendly. They are added to detergents so that dirt is removed even at low temperature, and they help make glucose and fructose syrup from corn flour. Antibiotics from bacteria and fungi, such as penicillin, streptomycin, tetracyclines and erythromycin, control many diseases; rifamycin is effective against tuberculosis.

Microbes give fuels: methane from anaerobic decomposition of waste, ethanol (a clean fuel) from fermentation of molasses by Saccharomyces, and hydrogen from bio-photolysis of water by bacteria. In landfill sites, compressed waste is dumped in plastic-lined pits, covered with soil and other layers, and decomposed by microbes into compost. In sewage treatment, microbes decompose carbon compounds releasing methane and CO2, destroy pathogens, and phenol-oxidizing bacteria break down xenobiotic chemicals; the sludge is used as fertilizer.

In clean technology, some microbes remove sulphur from fuels and thiobacilli help in metal leaching. Hydrocarbonoclastic bacteria such as Pseudomonas and Alcanovorax borkumensis clean oil spills by converting hydrocarbons into CO2 and water. Vibrio and Ideonella sakaiensis decompose PET plastic, and Actinomycetes, Streptomyces, Nocardia and Actinoplanes decompose rubber. Acidophilium and Acidobacillus ferroxidans use sulphuric acid from acid rain as an energy source, and Geobacter converts soluble uranium salts into insoluble ones. In farming, microbial inoculants such as Azotobacter supply nutrients and reduce pollution from chemical fertilizers, microbes destroy pesticides in soil, and bacterial and fungal toxins act as bioinsecticides; Spinosad is a biopesticide from fermentation.

Mind map

Industrial production of vinegar

Important definitions

Formulas

Key points to remember

• Most milk products are made with bacteria; only cheese involves fungi.
• Yoghurt bacteria: Streptococcus thermophilus and Lactobacillus delbrueckii in 1:1 ratio.
• Diacetyl gives butter flavour; acetaldehyde-like compounds give yoghurt its taste.
• Fungal protease is used instead of rennet to make vegetarian cheese.
• Cheddar ripens in 3 to 12 months; parmesan in 12 to 18 months.
• Probiotics reduce harmful microbes such as Clostridium.
• Baker's yeast is Saccharomyces cerevisiae.
• Vinegar is about 4% acetic acid; soya sauce uses Aspergillus oryzae.
• Xanthan gum is made by Xanthomonas; citric and gluconic acids by Aspergillus niger.
• Rifamycin is effective against tuberculosis.
• Hydrogen, released by bio-photolysis of water, is considered the fuel of the future.
• Pseudomonas and Alcanovorax borkumensis clean oil spills.
• Ideonella sakaiensis and Vibrio decompose PET plastic.
• Geobacter makes soluble uranium salts insoluble.
• Azotobacter is used in organic farming; Spinosad is a biopesticide.

Solved examples

Example 1. Explain step by step how industrial yoghurt is made.

1. Condensed milk powder is added to milk to keep up protein content. 2. Milk is boiled and allowed to cool to a warm temperature. 3. Streptococcus thermophilus and Lactobacillus delbrueckii are added in 1:1 proportion. 4. Lactic acid formed by Streptococcus makes the proteins gel, giving thick consistency. 5. Lactobacilli form acetaldehyde-like compounds that give taste. 6. Fruit juices may be added for flavour, and pasteurization improves shelf life.

Example 2. How does bread become spongy?

Flour is mixed with baker's yeast (Saccharomyces cerevisiae), water and salt to make dough. The yeast ferments carbohydrates and converts sugar into carbon dioxide and ethanol. The CO2 gas gets trapped in the dough and makes it rise. On baking, the gas spaces remain, so the bread becomes spongy.

Example 3. How can an oil spill in the sea be cleaned?

Removing an oil layer mechanically is difficult. Hydrocarbonoclastic bacteria such as Pseudomonas species and Alcanovorax borkumensis are used. They decompose hydrocarbons and other chemicals like pyridines, combining carbon with oxygen. The oil is converted into CO2 and water, which are harmless.

Example 4. How can soil polluted by acid rain be made fertile again?

Acid rain adds sulphuric acid to soil. Bacteria such as Acidophilium species and Acidobacillus ferroxidans use sulphuric acid as a source of energy. Adding these bacteria removes the acid, controls the soil pollution and helps the soil regain fertility.

Example 5. Explain how waste is processed in a modern landfill site.

1. A large pit is dug far from homes and lined with plastic sheet to prevent toxic leaching. 2. Compressed waste is dumped in it. 3. It is covered with layers of soil, saw dust, leafy waste and biochemicals; bioreactors may be added. 4. Microbes decompose the waste. 5. The filled pit is sealed with soil slurry. 6. Good compost forms in a few days, and the site can be reused after removing it.

Important questions and answers

Q1. Fill in: Process of ____ of milk proteins occurs due to lactic acid.

Coagulation.

Q2. Fill in: Chemically, vinegar is ____.

Acetic acid (about 4%).

Q3. Fill in: Salts used as supplements of calcium and iron are obtained from ____ acid.

Gluconic acid.

Q4. Match: Xylitol, Citric acid, Lycopene, Nycin.

Xylitol: to impart sweetness (low-calorie sweetener). Citric acid: to impart acidity. Lycopene: pigment (edible colour). Nycin: microbial restrictor.

Q5. Give reason: Use of mutant strains has increased in industrial microbiology.

Bacteria used in industry can be attacked by viruses, and some steps or materials in production are unnecessary. Artificially developed mutant and virus-resistant strains avoid these problems, so their use has increased.

Q6. Give reason: Enzymes obtained by microbial processes are mixed with detergents.

Microbial enzymes break down dirt and stains even at low temperature. So detergents containing them remove muck effectively without needing high temperature.

Q7. Give reason: Microbial enzymes are used instead of chemical catalysts in chemical industry.

They work at low temperature, pH and pressure, so energy is saved and corrosion-proof instruments are not needed. They are specific, so no unwanted by-products form and purification costs are low. They can be reused and do not create waste, so they are eco-friendly.

Q8. Which fuels can be obtained by microbial processes? Why should their use be increased?

Methane (from anaerobic decomposition of waste), ethanol (from fermentation of molasses by Saccharomyces) and hydrogen (from bio-photolysis of water by bacteria). They are renewable, easily available and cleaner; ethanol is smokeless. Their use reduces dependence on polluting fossil fuels.

Q9. Why are probiotic products becoming popular?

Probiotics form colonies of useful microbes in the alimentary canal, control harmful microbes and their metabolic activities, improve resistance, reduce ill-effects of harmful substances formed in metabolism, and reactivate useful microbes made inactive by antibiotics. They are also used to treat diarrhoea.

Q10. How are bread and other products made with baker's yeast nutritious?

Commercial yeast itself contains carbohydrates, fats, proteins, various vitamins and minerals. These are added to the bread, so the products become nutritive.

Q11. Explain the importance of bio-pesticides in organic farming.

Bacterial and fungal toxins that kill pests can be built into plants by biotechnology, so insects do not eat the plants. Some fungi and viruses also act as pesticides, and Spinosad is a fermentation by-product used as a biopesticide. They avoid harmful chemical pesticides such as fluoroacetamide that harm other organisms and cause skin diseases.

Q12. How is cheese made vegetarian today?

Earlier rennet from the alimentary canal of cattle was used to curdle milk. Now protease enzyme obtained from fungi is used instead, giving vegetarian cheese.

Exam tips

• Learn microbe names with their products as pairs: they are asked in match the pairs and fill in the blanks.
• For 'give reasons' on microbial enzymes, list the points: low temperature, specific, no by-products, reusable, eco-friendly.
• Write vinegar and yoghurt production as numbered steps.
• Remember examples for each pollution problem: oil spill, PET, rubber, acid rain, uranium.
• Spell scientific names correctly and mention the genus at least.

FAQs

Which microbe is used to make bread?

Baker's yeast, Saccharomyces cerevisiae.

What are hydrocarbonoclastic bacteria?

Bacteria such as Pseudomonas and Alcanovorax borkumensis that break down hydrocarbons into CO2 and water and are used to clear oil spills.

Which bacteria are used to make yoghurt industrially?

Streptococcus thermophilus and Lactobacillus delbrueckii, added in 1:1 proportion.

Which antibiotic is effective against tuberculosis?

Rifamycin.

These notes were prepared with AI help from the Balbharati Science and Technology Part 2 textbook (2026-27) and checked against it.