Microbes and Fermentation

6.1 Classification of Microbes

Type	Cell type	Examples	Role
Bacteria	Prokaryote	Lactobacillus, E. coli, Rhizobium, Mycobacterium	Curd, nitrogen fixation, disease, industrial
Fungi	Eukaryote	Saccharomyces (yeast), Penicillium, Aspergillus	Fermentation, antibiotics, enzymes
Algae	Eukaryote	Chlorella, Anabaena (cyanobacteria)	O₂ production, nitrogen fixation, food
Protozoa	Eukaryote	Plasmodium (malaria), Amoeba	Disease, research models
Viruses	Non-cellular	HIV, SARS-CoV-2, Influenza	Disease, gene therapy vectors
Prions	Protein only	BSE (mad cow), CJD	Misfolded proteins cause neurodegenerative disease

6.2 Fermentation

Fermentation is the anaerobic metabolic conversion of organic compounds (primarily sugars) by microbes to simpler molecules with production of ATP.

Alcoholic Fermentation (yeast — Saccharomyces cerevisiae)

• Equation: C₆H₁₂O₆ → 2C₂H₅OH (ethanol) + 2CO₂ + Energy (2 ATP)
• Commercial uses: beer, wine, whisky, rum; bioethanol for fuel; bread leavening (CO₂ makes bread rise)

Lactic Acid Fermentation (bacteria — Lactobacillus spp.)

• Equation: Glucose → Lactic acid (+ energy)
• Used in: yogurt/curd (Lactobacillus bulgaricus/thermophilus), cheese, silage, kimchi, sauerkraut

Industrial Fermentation

• Penicillin: Penicillium notatum/chrysogenum — industrial scale in bioreactors
• Citric acid: Aspergillus niger — food additive
• Recombinant human insulin: E. coli expressing human insulin gene — revolutionised diabetes treatment (1982, Humulin — first recombinant protein drug)
• Biofuels: Cellulosic biomass fermentation for second-generation bioethanol

6.3 Infectious Diseases

Disease	Pathogen	Transmission	Prevention
Tuberculosis (TB)	Mycobacterium tuberculosis	Airborne droplets	BCG vaccine; DOTS therapy
Malaria	Plasmodium spp. (P. falciparum most fatal)	Anopheles mosquito bite	Mosquito nets, antimalarials
COVID-19	SARS-CoV-2 (coronavirus)	Airborne, droplets	COVID-19 vaccines (mRNA, adenovirus-vector, inactivated)
Dengue	Dengue virus (4 serotypes)	Aedes aegypti mosquito	No vaccine widely available; vector control
Polio	Poliovirus (3 types)	Faecal-oral route	OPV (oral) or IPV (injectable)
Hepatitis B	HBV (DNA virus)	Blood, sexual, mother-to-child	Recombinant HBV vaccine

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