🌸Chapter 8
Microbes in Human Welfare
(Notes)
🔷 1. Introduction
- Microbes (Microorganisms): Tiny living organisms
invisible to the naked eye.
- Types of Microbes:
- Bacteria
- Fungi
- Protozoa
- Algae
- Viruses
- Viroids
- Prions
Though some microbes cause diseases, many are beneficial
to humans and play important roles in food processing, industrial
production, sewage treatment, agriculture, etc.
🔷 2. Microbes in Household
Products
🍶 (A) Fermented Beverages
- Microbes are used to convert sugar
into alcohol by the process of fermentation.
- Yeast (Saccharomyces
cerevisiae)
is commonly used.
Examples:
|
Beverage |
Substrate |
Organism |
|
Wine |
Grapes (fruit juice) |
Saccharomyces cerevisiae |
|
Beer |
Barley malt |
Saccharomyces cerevisiae |
|
Whisky, Rum, Brandy |
Molasses or grains |
Saccharomyces cerevisiae |
Note:
Different beverages have different alcohol content depending on substrate
and distillation process.
🍞 (B) Fermented Foods
(i) Bread Making:
- Yeast → ferments dough → CO₂
produced → dough rises → soft and spongy texture.
(ii) Idli, Dosa, Dhokla:
- Fermentation by Lactic Acid
Bacteria (LAB) and Yeast.
- Increases digestibility and
nutrient value.
🥛 (C) Curd Formation:
- Curd prepared by Lactic Acid
Bacteria (Lactobacillus / Lactococcus).
- LAB ferments lactose (milk
sugar) into lactic acid.
- Lactic acid → coagulates milk
protein (casein) → curd.
- Improves nutritional quality
and vitamin B12 content.
NEET Tip:
Starter culture of curd contains Lactobacillus
acidophilus.
🧈 (D) Other Dairy Products:
- Cheese: Different microbes give
characteristic texture and flavour.
- Roquefort cheese → ripened by Penicillium
roqueforti.
- Swiss cheese → by Propionibacterium
shermanii (produces CO₂ → holes in cheese).
🔷 3. Microbes in Industrial
Products
Industrial microbiology involves large-scale microbial
growth in fermenters to produce useful products.
Major Industrial Products:
|
Product |
Example Organism |
Use |
|
Alcoholic Beverages |
Saccharomyces cerevisiae |
Drinks, solvents |
|
Antibiotics |
Penicillium notatum, Streptomyces spp. |
Kill/inhibit bacteria |
|
Organic Acids |
Aspergillus niger (citric acid), Acetobacter aceti (acetic acid), Clostridium
butylicum (butyric acid) |
Food, industry |
|
Enzymes |
Aspergillus spp., Bacillus spp. |
Detergents, textile, food |
|
Cyclosporin A |
Trichoderma polysporum |
Immunosuppressant (used in organ transplantation) |
|
Statins |
Monascus purpureus |
Lowers blood cholesterol |
🧫 (A) Antibiotics
- Definition: Chemical substances produced
by microorganisms that kill or inhibit growth of other microbes.
- First antibiotic: Penicillin discovered
by Alexander Fleming (1928) from Penicillium notatum.
- Florey and Chain → developed it for large-scale
use (WWII).
- Importance: Revolutionized medicine; saved
millions of lives.
Examples:
·
Streptomycin
(from Streptomyces griseus)
·
Tetracycline,
Erythromycin, Chloramphenicol, etc.
⚗️ (B) Fermenters
- Large vessels (stainless steel)
used for industrial-scale microbial culture under controlled conditions
(temperature, aeration, pH).
- Products extracted, purified,
and commercialized.
🔷 4. Microbes in Sewage
Treatment
🧴 (A) Sewage:
- Wastewater from homes,
hospitals, industries → contains organic matter & microbes.
🧪 (B) Sewage Treatment
Steps:
(i) Primary Treatment (Physical)
- Removal of large and
floating particles by filtration & sedimentation.
- Solids → primary sludge
- Supernatant → effluent
(used in secondary treatment).
(ii) Secondary Treatment
(Biological)
- Effluent passed into aeration
tanks → aerobic microbes oxidize organic matter → CO₂ + water.
👉 Involves formation of Activated Sludge:
- Microbes form flocs
(masses of bacteria + fungal filaments).
- Effluent → aerated → microbes
consume organic matter.
- After settling → activated
sludge formed (used as inoculum).
Some activated sludge → used to treat new sewage; remainder
→ digested anaerobically → biogas.
(iii) Anaerobic Sludge Digestion:
- Methanogens (Archaebacteria) like Methanobacterium
act on sludge.
- Produce biogas (CH₄ +
CO₂ + H₂).
Diagram (for Boards & NEET):
Sewage Treatment → Primary
(Physical) → Secondary (Biological)
↓ ↓
Primary Sludge Activated Sludge → Biogas
🔷 5. Microbes in Production
of Biogas
- Biogas: Mixture of methane (CH₄),
CO₂, and H₂ produced by microbial anaerobic digestion.
(A) Biogas Production Process
1.
Slurry
of cow dung + water
→ put in biogas plant digester.
2.
Anaerobic
digestion by
methanogenic bacteria → Methanobacterium.
3.
Biogas collected from top chamber and used
as fuel.
Steps of Digestion:
1.
Hydrolysis
2.
Acid
formation
3.
Methane
formation
Uses:
- Cooking, lighting, running
engines.
- Reduces pollution and provides
manure.
Developed in India by Indian Agricultural Research
Institute (IARI) and Khadi and Village Industries Commission (KVIC).
🔷 6. Microbes as Biocontrol
Agents
🐞 Definition:
Use of natural living organisms (microbes, insects,
etc.) to control pests and diseases.
Examples:
|
Biocontrol Agent |
Organism |
Target / Use |
|
Bacillus thuringiensis (Bt) |
Bacterium |
Insect pest control (kills larvae of butterfly, moth,
beetle) |
|
Trichoderma spp. |
Fungi |
Free-living fungi in root region → control fungal
pathogens |
|
Ladybird beetle, Dragonfly |
Insects |
Eat aphids and mosquitoes (biological pest control) |
Bt toxin
gene has been used to produce Bt cotton (GM crop) resistant to bollworm.
🔷 7. Microbes as
Biofertilisers
🌱 Definition:
Microorganisms that increase soil fertility and plant
growth by enriching nutrient availability.
Major Categories:
(i) Bacteria
- Rhizobium → lives symbiotically in root
nodules of leguminous plants → fixes nitrogen.
- Azospirillum, Azotobacter → free-living
nitrogen fixers.
(ii) Cyanobacteria (Blue-green
algae)
- Anabaena, Nostoc, Oscillatoria
→ photosynthetic, fix N₂.
- Found in paddy fields →
increase yield naturally.
(iii) Fungi (Mycorrhiza)
- Glomus forms symbiotic association
with plant roots.
- Help in phosphate absorption,
water uptake, and disease resistance.
(iv) Biofertilizer Mixtures
- Contain combinations like Rhizobium
+ Phosphate-solubilizing bacteria + Azotobacter for balanced nutrient
supply.
🔷 8. Summary Table (NEET
Revision Sheet)
|
Role |
Microbe |
Application |
|
Curd |
Lactobacillus |
Milk → Curd |
|
Bread |
Saccharomyces cerevisiae |
Dough fermentation |
|
Swiss Cheese |
Propionibacterium shermanii |
CO₂ → holes |
|
Antibiotic |
Penicillium notatum |
Penicillin |
|
Organic Acid |
Aspergillus niger |
Citric acid |
|
Immunosuppressant |
Trichoderma polysporum |
Cyclosporin A |
|
Cholesterol lowering |
Monascus purpureus |
Statins |
|
Sewage Treatment |
Methanobacterium |
Biogas |
|
Biofertiliser |
Rhizobium |
N₂ fixation |
|
Bt Toxin |
Bacillus thuringiensis |
Biopesticide |
🔷 9. Important Diagrams (for
Board Exam)
1.
Sewage
treatment plant (aeration tank)
2.
Biogas
plant structure
3.
Root
nodule showing Rhizobium
4.
Activated
sludge process (flow chart)
🔷 10. NEET & Board
Important Keywords
Fermentation, Antibiotic, Flocs, Activated sludge,
Methanogens, Biogas, Biofertiliser, Mycorrhiza, Bt toxin, Cyclosporin A,
Statins, Lactic acid bacteria.
🧠 Important Board / NEET
Questions
1.
What
is the role of Lactobacillus in milk?
→ Converts lactose into lactic acid; coagulates milk → curd formation.
2.
Name
one methanogen and its function.
→ Methanobacterium → produces biogas during anaerobic digestion.
3.
What
are antibiotics? Give one example.
→ Chemical substances from microbes that kill/inhibit other microbes; e.g., Penicillin.
4.
What
is the function of Trichoderma?
→ Fungal biocontrol agent → suppresses pathogens in root region.
5.
What
are biofertilisers? Give examples.
→ Microbes that enhance soil fertility; e.g., Rhizobium, Anabaena,
Mycorrhiza.
✳️ Quick Revision (Before Exam)
- Curd → Lactobacillus
- Bread → Yeast
- Cheese → Propionibacterium
- Antibiotic → Penicillin
- Acid → Citric (Aspergillus),
Acetic (Acetobacter)
- Immunosuppressant → Cyclosporin
A
- Cholesterol ↓ → Statins
- Sewage → Methanogens
- Biogas → Methanobacterium
- Biopesticide → Bt toxin
- Biofertiliser → Rhizobium,
Anabaena, Mycorrhiza
