2.1 Microbes in Food Processing

Lactic acid bacteria (LAB), particularly Lactobacillus, ferment milk lactose to lactic acid, causing milk protein casein to coagulate into curd. This process also elevates vitamin B12 concentration. Saccharomyces cerevisiae (baker's/brewer's yeast) performs alcoholic fermentation: producing CO2 (leavens dough) and ethanol (in beer and wine). Cheese-making exploits specific microbes for distinct outcomes — Propionibacterium shermanii makes Swiss cheese holes through CO2, Penicillium roqueforti makes Roquefort cheese through blue mold ripening. Aspergillus niger produces citric acid; Acetobacter aceti produces acetic acid (vinegar) by oxidizing ethanol.

2.2 Microbes in Industrial Products

Three categories of industrial microbial products:

Antibiotics: Penicillin (Penicillium notatum, discovered 1928 by Fleming), streptomycin, erythromycin, tetracycline (all from Streptomyces species).

Enzymes: Streptokinase from Streptococcus — thrombolytic, dissolves blood clots (NOT an antibiotic). Lipases and proteases from bacteria and fungi — used in detergents. Pectinases from Aspergillus — clarify fruit juices.

Bioactive Molecules: Lovastatin (statin) from Monascus purpureus — inhibits HMG-CoA reductase, lowers cholesterol. Cyclosporin A from Trichoderma polysporum — immunosuppressant for organ transplants.

2.3 Microbes in Sewage Treatment

Two-stage treatment plus anaerobic digestion:

• Primary (physical): Screening → grit removal → sedimentation → primary sludge + primary effluent
• Secondary (biological): Aeration tanks with aerobic microbes → BOD reduction → settling → activated sludge (recycled or digested)
• Anaerobic digestion: Methanogens (Methanobacterium) → biogas (CH4 + CO2 + H2S)

BOD = dissolved O2 consumed by microbial decomposition; high BOD = greater pollution.

2.4 Microbes as Biocontrol Agents

• Bacillus thuringiensis (Bt): Cry proteins toxic to lepidopteran larvae; basis of Bt crops
• Baculoviruses (NPV): species-specific insect pathogens; safe for non-target organisms
• Trichoderma: fungal control of soil-borne plant pathogens
• Ladybird beetles: biological predators of aphids

2.5 Microbes as Biofertilizers

• Rhizobium: symbiotic N2 fixation in legume root nodules
• Azotobacter / Azospirillum: free-living (non-symbiotic) N2 fixation
• Anabaena / Nostoc (cyanobacteria): N2 fixation + organic matter addition in paddy fields
• Glomus (mycorrhiza): symbiotic fungus enhancing phosphorus uptake (NOT N2 fixation)