Microbes in Human Welfare — Short Notes
Microbes are useful for food production, industrial products, sewage treatment, biogas, biocontrol, and biofertilisers.
Microbes in Household Products
Curd
- **Lactic Acid Bacteria (LAB) — Lactobacillus** ferment milk → coagulate → curd.
- Also improves Vitamin B₁₂ content and helps in stomach infection resistance.
Dough (idli, dosa, bhaturas)
- Fermented by bacteria + yeast.
- CO₂ released → puffing.
Cheese
- Swiss cheese — large holes from CO₂ produced by Propionibacterium shermanii.
- Roquefort cheese — ripened by Penicillium roqueforti.
Bread
- Saccharomyces cerevisiae (baker's yeast).
Toddy
- Fermenting palm sap by yeast.
Microbes in Industrial Products
Fermented beverages
- Saccharomyces cerevisiae (brewer's yeast) ferments sugars → ethanol + CO₂.
- Types:
- Wine, beer — without distillation.
- Whisky, brandy, rum — with distillation.
Antibiotics
- Penicillin — from Penicillium notatum; discovered by Alexander Fleming (1928); Chain & Florey developed it as antibiotic.
- Used in WWII (against wounded soldiers' infections).
- Antibiotics inhibit or kill pathogens without harming human cells (selective toxicity).
Chemicals, Enzymes, Bioactive molecules
| Product | Microbe | Use |
|---|---|---|
| Citric acid | Aspergillus niger | Food preservation |
| Acetic acid | Acetobacter aceti | Vinegar |
| Butyric acid | Clostridium butylicum | Chemical industry |
| Lactic acid | Lactobacillus | Foods |
| Ethanol | Saccharomyces cerevisiae | Fuel, beverages |
| Lipase | Fungi/bacteria | Detergents (removes oil stains) |
| Pectinase, protease | Fungi | Clarify fruit juices |
| Streptokinase | Streptococcus | Clot buster in heart-attack patients |
| Cyclosporin-A | Trichoderma polysporum | Immunosuppressant in transplants |
| Statins | Monascus purpureus | Lower blood cholesterol |
Microbes in Sewage Treatment
Sewage = municipal waste with BOD-heavy organic material and pathogens.
Primary treatment
- Physical — filtration + sedimentation → primary sludge + effluent.
Secondary (biological) treatment
- Effluent aerated in aeration tank → flocs of aerobic bacteria grow (fungi + bacteria clumps).
- BOD drops significantly.
- Mixture goes to settling tank → activated sludge settles.
- Some sludge → aeration tank as inoculum; rest → anaerobic sludge digesters.
- Anaerobic microbes produce biogas (CH₄, H₂S, CO₂).
Tertiary treatment
- Chemical treatment before release (removes N, P, pathogens).
Microbes in Biogas Production
- Biogas — CH₄ + CO₂ + H₂ (+ small H₂S).
- Methanogens — Methanobacterium — anaerobic; found in cattle rumen and sewage.
- Cattle dung (gobar) is the main substrate.
- Biogas plants (KVIC & IARI designs) — provides fuel and slurry that acts as manure.
Microbes as Biocontrol Agents
Insects and diseases (biological pest control)
- Ladybird beetles & Dragonflies — control aphids and mosquitoes.
- Bacillus thuringiensis (Bt) — kills butterfly caterpillars; used as spray or in Bt cotton.
- Trichoderma (fungus) — free-living on roots; controls plant pathogens.
- Baculoviruses (Nucleopolyhedrovirus) — species-specific insecticide; safe for other organisms.
Microbes as Biofertilisers
- Enrich soil nutrients naturally.
Nitrogen-fixing bacteria
- Rhizobium — root nodules of legumes → fixes atmospheric N₂.
- ***Azotobacter*, Azospirillum** — free-living in soil.
- Cyanobacteria — ***Anabaena*, Nostoc, Oscillatoria** — fix N₂ in paddy fields.
- Azolla — floating fern with symbiotic Anabaena — used in rice fields.
Mycorrhiza
- Symbiosis between fungi (Glomus) and plant roots.
- Absorbs P and other nutrients; increases drought/disease tolerance.
Take-aways
- Microbes are beneficial partners in food, medicine, industry, waste management, and agriculture.
- Alexander Fleming's discovery of penicillin transformed medicine.
- Sewage plants and biogas plants exploit microbial metabolism for public utility.
- Biofertilisers and biocontrol reduce chemical pollution in agriculture.