Microbes in Human Welfare

Key Concepts

Microbes in Household Products

Microbes or their products are part of our daily lives.

• Curd: Lactobacillus (LAB - Lactic Acid Bacteria) converts milk to curd, increases Vitamin B12, and checks disease-causing microbes in the stomach.
• Dough: Puffed-up appearance of dosa/idli dough is due to CO2 production by bacteria. Bread is fermented using Baker’s yeast (Saccharomyces cerevisiae).
• Toddy: Traditional drink made by fermenting palm sap.
• Cheese:
  • Swiss Cheese: Large holes due to CO2 from Propionibacterium sharmanii.
  • Roquefort Cheese: Ripened by specific fungi for flavour.

Microbes in Industrial Products

Requires large vessels called fermentors.

• Fermented Beverages: Brewer’s yeast (S. cerevisiae) is used for ethanol production from malted cereals/fruit juices. (Distilled: Whisky, Brandy, Rum; Undistilled: Wine, Beer).
• Antibiotics: Chemical substances produced by microbes to kill/retard other microbes.
  • Penicillin: First antibiotic, discovered by Alexander Fleming (from Penicillium notatum). Chain and Florey established its full potential.
• Chemicals and Enzymes:
  • Citric Acid: Aspergillus niger (fungus).
  • Acetic Acid: Acetobacter aceti (bacterium).
  • Butyric Acid: Clostridium butylicum (bacterium).
  • Lipases: Used in detergents (remove oil stains).
  • Pectinases/Proteases: Clarify bottled fruit juices.
  • Streptokinase: 'Clot buster' for heart attack patients.
• Bioactive Molecules:
  • Cyclosporin A: Immunosuppressive agent from Trichoderma polysporum.
  • Statins: Blood-cholesterol lowering agents from Monascus purpureus.

Microbes in Sewage Treatment

• Primary Treatment: Physical removal of particles (filtration and sedimentation). Supernatant forms the effluent.
• Secondary (Biological) Treatment:
  • Effluent passed to aeration tanks; aerobic microbes form flocs.
  • Microbes consume organic matter, reducing BOD (Biochemical Oxygen Demand).
  • Greater BOD = More polluting potential.
  • Activated Sludge: Sedimented flocs.
  • Anaerobic Sludge Digesters: Anaerobic bacteria produce Biogas (CH4, H2S, CO2).

Microbes in Biogas Production

• Methanogens: e.g., Methanobacterium. Produce methane anaerobically on cellulosic material.
• Found in anaerobic sludge and the rumen of cattle (helps digest cellulose).
• Biogas Plant: Uses cattle dung (gobar) to produce gas for cooking and lighting.

Microbes as Biocontrol Agents

Use of biological methods to control pests/diseases, reducing chemical use.

• Bacillus thuringiensis (Bt): Controls butterfly caterpillars (toxin released in larvae gut).
• Trichoderma: Free-living fungi in root ecosystems; control several plant pathogens.
• Baculoviruses (Nucleopolyhedrovirus): Species-specific, narrow-spectrum insecticidal application; no harm to non-target organisms.

Microbes as Biofertilisers

Organisms that enrich soil nutrient quality.

• Bacteria: Rhizobium (symbiotic in legume nodules), Azospirillum, Azotobacter (free-living).
• Fungi: Glomus forms Mycorrhiza; absorbs phosphorus and provides resistance to root pathogens/drought.
• Cyanobacteria: Anabaena, Nostoc, Oscillatoria. Fix atmospheric nitrogen, important in paddy fields.