Useful microbes help us in six areas: household products, industrial products, sewage treatment, biogas production, biocontrol and biofertilisers.
1. Microbes in household products
Product
Microbe
What it does
Curd
Lactobacillus and other lactic acid bacteria (LAB)
Make lactic acid, which curdles milk. Also increase vitamin B₁₂ and kill harmful germs in the stomach
Idli / dosa batter
Bacteria
Fermentation makes CO₂, so the batter becomes puffy
Bread
Baker's yeast (Saccharomyces cerevisiae)
Fermentation makes CO₂, so the dough rises
Toddy
Microbes
A traditional drink from southern India, made by fermenting palm sap
Swiss cheese
Propionibacterium sharmanii
Makes lots of CO₂, which creates the big holes
Roquefort cheese
Fungi
Ripen the cheese and give it flavour
2. Microbes in industry
Fermented drinks
Brewer's yeast (Saccharomyces cerevisiae) ferments fruit juices and grains.
Without distillation:wine and beer.
With distillation:whisky, brandy and rum (they have more alcohol).
Antibiotics
Antibiotic means "against life". Antibiotics are chemicals made by microbes that kill or stop disease-causing microbes.
Chemicals, enzymes and medicines
Product
Microbe
Type
Use
Citric acid
Aspergillus niger
Fungus
Food flavour
Acetic acid (vinegar)
Acetobacter aceti
Bacterium
Vinegar
Butyric acid
Clostridium butylicum
Bacterium
—
Lactic acid
Lactobacillus
Bacterium
—
Ethanol
Saccharomyces cerevisiae
Yeast
Alcohol, fuel
Lipases
Microbes
Enzyme
In detergents: remove oily stains
Pectinases, proteases
Microbes
Enzyme
Make bottled fruit juices clear
Streptokinase
Streptococcus
Bacterium
"Clot buster": removes blood clots in heart-attack patients
Cyclosporin A
Trichoderma polysporum
Fungus
Immunosuppressant in organ transplants
Statins
Monascus purpureus
Yeast
Lower blood cholesterol
3. Microbes in sewage treatment
Primary treatment (physical): filtering and settling remove grit, soil and pebbles. The settled solids form primary sludge; the liquid on top is the primary effluent.
Secondary treatment (biological): the effluent is aerated. Aerobic microbes grow as flocs and eat the organic matter, so the BOD falls.
The flocs settle as activated sludge:
a small part goes back into the aeration tank as inoculum;
most goes to anaerobic sludge digesters, where bacteria produce biogas.
The treated water is released into rivers.
Flocs are clumps of bacteria + fungal threads, like tiny "cleaning teams".
BOD (Biochemical Oxygen Demand): the amount of oxygen that microbes would use to break down all the organic matter in one litre of water.
The Ministry of Environment and Forests started the Ganga Action Plan and the Yamuna Action Plan to save these rivers from pollution.
4. Microbes in biogas production
Biogas is mostly methane (CH₄), with some CO₂ and H₂S. It burns well and is used for cooking and lighting.
It is made by methanogens (e.g. Methanobacterium). These bacteria live without oxygen (anaerobic).
They are found in cow dung (gobar) and in the rumen (stomach) of cattle, where they help digest cellulose.
Cow dung slurry → digester tank (no oxygen) → methanogens act → biogas (mainly CH₄) for cooking. The spent slurry is used as fertiliser.
The biogas technology in India was developed mainly by IARI (Indian Agricultural Research Institute) and KVIC (Khadi and Village Industries Commission).
5. Microbes as biocontrol agents
Biocontrol agent
Controls
Ladybird beetle
Aphids
Dragonflies
Mosquitoes
Bacillus thuringiensis (Bt)
Caterpillars (butterfly larvae). Its toxin kills them in their gut
Trichoderma (fungus)
Plant disease germs (pathogens) in the soil
Baculoviruses (Nucleopolyhedrovirus)
Insects and other arthropods. Species-specific, so they don't harm useful insects
IPM (Integrated Pest Management): using many eco-friendly methods together instead of only chemicals.
6. Microbes as biofertilisers
Group
Examples
How they help
Symbiotic bacteria
Rhizobium (in root nodules of legumes like peas and beans)
Fix nitrogen from the air
Free-living bacteria
Azospirillum, Azotobacter (in soil)
Fix nitrogen
Fungi (mycorrhiza)
Glomus
Absorb phosphorus for the plant; protect roots from germs; help survive drought and salt
Cyanobacteria (blue-green algae)
Anabaena, Nostoc, Oscillatoria
Fix nitrogen, very important in rice (paddy) fields