Microbes in Human Welfare

Microbes serve humanity across food production, industrial manufacturing, waste management, pest control, and soil fertility. NEET consistently tests microbe-product associations, sewage treatment processes, and the BOD concept.

In food processing, Lactobacillus converts milk into curd through lactic acid fermentation and simultaneously increases vitamin B₁₂ content. Saccharomyces cerevisiae (baker's yeast) leavens dough by producing CO₂ and generates ethanol during brewing and winemaking. Cheese production involves specific microbes: Propionibacterium shermanii produces the large holes in Swiss cheese through CO₂ generation, while Penicillium roqueforti gives Roquefort cheese its characteristic blue-green ripening. Aspergillus niger produces citric acid, and Acetobacter aceti converts ethanol to acetic acid (vinegar).

Industrial microbiology yields antibiotics, enzymes, and bioactive molecules. Alexander Fleming discovered penicillin from Penicillium notatum in 1928. Streptomyces species produce streptomycin, erythromycin, and tetracycline. Key enzymes include streptokinase (from Streptococcus, used as a thrombolytic clot-buster — not an antibiotic), lipases and proteases (used in laundry detergents), and pectinases (for clarifying fruit juices). Among bioactive molecules, statins from Monascus purpureus (particularly lovastatin) lower blood cholesterol by competitively inhibiting HMG-CoA reductase. Cyclosporin A, produced by Trichoderma polysporum, acts as an immunosuppressant crucial for organ transplant success.

Sewage treatment proceeds in defined stages. Primary treatment is physical: screening, grit removal, and sedimentation separate primary sludge (settled solids) from primary effluent (liquid supernatant). Secondary treatment is biological: primary effluent enters aeration tanks where aerobic microbes vigorously grow, consuming organic matter and reducing BOD (Biochemical Oxygen Demand). The resulting activated sludge settles in a settling tank — a portion is recycled as inoculum, and the rest enters anaerobic digesters. BOD measures the amount of dissolved oxygen consumed by microbes to decompose organic matter in water; high BOD indicates greater pollution. Anaerobic digestion by methanogens (especially Methanobacterium) converts sludge into biogas — a mixture of methane, CO₂, and H₂S.

Biocontrol agents offer targeted pest management. Bacillus thuringiensis (Bt) produces crystalline Cry proteins (Cry1Ac, Cry2Ab) that are toxic to lepidopteran insect larvae — the foundation of Bt crop technology. Baculoviruses, particularly Nucleopolyhedrovirus (NPV), attack insects with high species-specificity and do not harm non-target organisms. Trichoderma controls soil-borne plant pathogens, while ladybird beetles (coccinellids) consume aphids.

Biofertilizers enhance soil fertility biologically. Rhizobium establishes symbiotic nitrogen fixation within legume root nodules. Free-living nitrogen fixers include Azotobacter and Azospirillum. Cyanobacteria such as Anabaena and Nostoc fix atmospheric nitrogen and contribute organic matter — they are particularly important in paddy fields. Mycorrhiza (e.g., Glomus) is a symbiotic fungus-root association that primarily enhances phosphorus uptake (not nitrogen), along with improving water absorption and disease resistance.

The key testable concept is the precise microbe-product association — particularly that Propionibacterium makes Swiss cheese holes (not Lactobacillus), streptokinase comes from Streptococcus (as a clot-buster, not an antibiotic), and mycorrhiza enhances phosphorus absorption (not nitrogen).