🧫 Microbes in Human Welfare & Applied Microbiology

Microorganisms (bacteria, fungi, viruses, and cyanobacteria) serve as microscopic biochemical factories synthesizing fermented foods, industrial chemicals, pharmaceuticals, enzymes, biofertilizers, and renewable energy.

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1. 🍶 Household & Industrial Microbial Fermentation

Product Category	Commercial Compound / Food	Microorganism Employed	Biochemical Mechanism / Application
Fermented Food	Curd	Lactobacillus / Lactic Acid Bacteria (LAB)	Coagulates milk casein protein; improves nutritional value by increasing Vitamin $B_{12}$.
Bakery / Brewing	Bread & Beer / Wine	Saccharomyces cerevisiae (Baker's / Brewer's Yeast)	Anaerobic fermentation of malted cereals/fruit juices into ethanol and $C{O}_2$ (puffs up dough).
Swiss Cheese	Large eye holes in cheese	Propionibacterium shermanii	Fermentation releases massive volumes of carbon dioxide ($C{O}_2$).
Roquefort Cheese	Characteristic flavor	Penicillium roqueforti	Ripened with fungal mycelium.
Organic Acid	Citric Acid	Aspergillus niger (Fungus)	Food preservative and flavor enhancer.
Organic Acid	Acetic Acid	Acetobacter aceti (Bacterium)	Vinegar production.
Organic Acid	Butyric Acid	Clostridium butyricum (Bacterium)	Industrial solvent and ester synthesis.
Organic Acid	Lactic Acid	Lactobacillus (Bacterium)	Food fermentation and biomaterials.
Enzyme	Lipases	Candida lipolytica	Used in detergent formulations to remove oily stains from laundry.
Enzyme	Pectinases & Proteases	Microbial blends	Used for clarifying bottled commercial fruit juices.
Enzyme (Clot Buster)	Streptokinase	Streptococcus (Bacterium)	Genetically modified to clear blood clots from vessels of patients with myocardial infarction.
Bioactive Molecule	Cyclosporin A	Trichoderma polysporum (Fungus)	Potent immunosuppressive agent used in organ transplantation.
Bioactive Molecule	Statins	Monascus purpureus (Yeast)	Blood cholesterol-lowering agent (competitively inhibits HMG-CoA reductase enzyme).

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2. 🚯 Microbes in Sewage Treatment Plants (STP)

                       SEWAGE TREATMENT FLOW PROCESS
  Raw Sewage ──► [Primary Treatment: Physical Screening & Sequential Sedimentation]
                                           │
                                           ▼ (Primary Effluent)
  [Secondary / Biological Treatment: Aerobic Aeration Tanks]
  - Vigorous mechanical agitation + air pumping
  - Formation of **Flocs** (Masses of bacteria associated with fungal filaments)
  - Microbes consume organic matter ──► **DRAMATIC DROP IN BOD (Biochemical Oxygen Demand)**!
                                           │
                                           ▼ (Secondary Effluent)
  [Settling Tank: Flocs sediment into ACTIVATED SLUDGE]
        │
        ├──► Small portion pumped back into aeration tank as **Inoculum**
        │
        ▼ (Major portion)
  [Anaerobic Sludge Digester]
  - Anaerobic methanogens (*Methanobacterium*) digest bacteria & fungi
  - Generates **Biogas (Methane $CH_4$, $CO_2$, $H_2S$)**

$$\text{High BOD}⟹\text{High Organic Pollution}⟹\text{Low Dissolved Oxygen (DO)}$$

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3. 🌾 Microbes as Biofertilizers & Biocontrol Agents

1. Nitrogen Fixers:
   • Symbiotic: Rhizobium in legume root nodules; Frankia in non-leguminous Alnus roots; Anabaena azollae in Azolla water fern (boosts paddy yields by $50\text{\%}$).
   • Free-living: Azotobacter, Azospirillum, Nostoc, Oscillatoria.
2. Mycorrhizae:
   • Fungal symbiont (primarily genus Glomus) absorbs phosphorus from soil and passes it to host roots; confers resistance to root-borne pathogens, salinity, and drought tolerance.
3. Biocontrol Agents:
   • Ladybird beetle controls Aphids; Dragonflies control Mosquitoes.
   • Bacillus thuringiensis (Bt): Spores sprayed to kill butterfly caterpillars.
   • Trichoderma fungi: Root ecosystem biocontrol against fungal plant pathogens.
   • Baculoviruses (Nucleopolyhedrovirus): Species-specific, narrow-spectrum insecticidal pathogens with zero negative impacts on non-target plants, mammals, birds, or beneficial pollinator insects.