10.1 Microbes in Household & Industrial Products
1. Household Products
- Curd: Lactic Acid Bacteria (LAB/Lactobacillus) grow in milk and convert it to curd by producing acids that coagulate and partially digest milk proteins. LAB improves nutritional value by increasing **Vitamin B12** and checks disease-causing microbes in the stomach.
- Dough: Fermented by bacteria (producing CO2 which causes puffed-up appearance) for Dosa/Idli. Bread dough is fermented by **Baker's yeast** (Saccharomyces cerevisiae).
- Cheese:
- Swiss Cheese: Has large holes due to high production of CO2 by the bacterium Propionibacterium sharmanii.
- Roquefort Cheese: Ripened by growing a specific fungus on them for a particular flavour.
2. Industrial Products
Grown in very large vessels called **fermentors**.
- Fermented Beverages: Brewer's yeast (Saccharomyces cerevisiae) ferments malted cereals and fruit juices into ethanol. Wine and Beer are produced **without distillation**, while Whisky, Brandy, and Rum are produced **by distillation** of the fermented broth.
- Antibiotics: **Penicillin** was discovered by Alexander Fleming while working on Staphylococcus bacteria (mould was Penicillium notatum). Its full potential was established by Ernest Chain and Howard Florey (Nobel Prize in 1945).
10.2 Chemicals, Enzymes & Bioactive Molecules
1. Organic Acids
| Acid | Microbe Source | Type |
|---|
| Citric Acid | Aspergillus niger | Fungus |
| Acetic Acid | Acetobacter aceti | Bacterium |
| Butyric Acid | Clostridium butylicum | Bacterium |
| Lactic Acid | Lactobacillus | Bacterium |
2. Enzymes & Applications
- Lipases: Used in detergent formulations to remove oily stains from laundry.
- Pectinases & Proteases: Used to clear bottled fruit juices.
- Streptokinase: Produced by Streptococcus bacterium. Modified genetically, it is used as a **"clot buster"** to remove blood clots from vessels in patients with myocardial infarction (heart attack).
3. Bioactive Molecules
- Cyclosporin A: Produced by the fungus Trichoderma polysporum. Used as an **immunosuppressive agent** in organ-transplant patients.
- Statins: Produced by the yeast Monascus purpureus. Used as **blood-cholesterol lowering agents** by competitively inhibiting the enzyme responsible for cholesterol synthesis.
10.3 Microbes in Sewage Treatment
Sewage contains large amounts of organic matter and pathogenic microbes. It is treated in **Sewage Treatment Plants (STPs)** before discharge.
1. Primary Treatment (Physical)
Physical removal of large and small particles through sequential filtration (removes floating debris) and sedimentation (removes grit/soil). Settled solids form **primary sludge**; supernatant is the **effluent**.
2. Secondary Treatment (Biological)
Effluent aerated and agitated→
Aerobic microbes form 'Flocs'→
Flocs consume organic matter→
BOD drops significantly
- Flocs: Masses of bacteria associated with fungal filaments to form mesh-like structures.
- BOD (Biochemical Oxygen Demand): The amount of oxygen consumed if all organic matter in 1 litre of water were oxidised by bacteria. Higher BOD = higher polluting potential.
- Once BOD drops, effluent is passed to a settling tank where flocs sediment as **activated sludge**.
- A small part of activated sludge is pumped back to the aeration tank (inoculum); the rest goes to **anaerobic sludge digesters**.
- Anaerobic bacteria digest flocs, producing **biogas** (mixture of **Methane (CH4), Hydrogen Sulfide (H2S), and CO2**).
10.4 Biogas, Biocontrol & Biofertilisers
1. Biogas Production
Biogas is a gas mixture produced by microbial activity. Major gas is methane, produced by anaerobic methanogens like Methanobacterium (found in cattle rumen and anaerobic sludge). Biogas plants ferment cow dung ('Gobar gas').
2. Microbes as Biocontrol Agents
- Ladybird beetles control aphids; Dragonflies control mosquitoes.
- Bacillus thuringiensis (Bt): Dry spores mixed with water are sprayed on plants. Caterpillars eat them, and the toxin is activated in their **alkaline gut**, killing them.
- Trichoderma: Free-living fungi in root ecosystems; act as effective biocontrol agents against several plant pathogens.
- Baculoviruses (Nucleopolyhedrovirus): Species-specific, narrow-spectrum insecticidal pathogens. Safe for mammals, birds, and non-target insects; ideal for **IPM (Integrated Pest Management)**.
3. Microbes as Biofertilisers
- Bacteria: Symbiotic Rhizobium in legume root nodules. Free-living nitrogen fixers like Azotobacter and Azospirillum.
- Fungi (Mycorrhiza): Fungi of genus Glomus form symbiotic associations with roots. The fungus absorbs **phosphorus** from the soil and transfers it to the plant, also conferring drought and salinity tolerance.
- Cyanobacteria: Autotrophic nitrogen fixers in aquatic/terrestrial habitats (e.g., Anabaena, Nostoc, Oscillatoria). Crucial biofertilisers in paddy fields.