Microbes in Human Welfare

1. Microbes in Household Products & Industrial Fermentation

A. Microbes in Household Products

• 1. Curd Formation: Lactobacillus / Lactic Acid Bacteria (LAB) converts milk sugar (lactose) to lactic acid, coagulating and partially digesting milk protein Casein.

  • LAB added as starter/inoculum. Checks disease-causing microbes in gut and enriches nutritional quality by increasing Vitamin $\text{B}_{12}$.

• 2. Cheese Production:

  • Swiss Cheese: Large holes produced due to high production of $\text{CO}_2$ by bacterium Propionibacterium shermanii.

  • Roquefort Cheese: Ripened by growing specific fungus Penicillium roqueforti on them for characteristic flavor.

• 3. Dosa, Idli & Bread: Dough fermented by bacteria/yeast produces $\text{CO}_2$ gas, giving a puffed-up appearance.

  • Baker’s Yeast (Saccharomyces cerevisiae): Used for bread making.

  • Fermented Foods: Soyabean, Fish, and Bamboo shoots fermented to make Tofu, Sofu, etc.

• 4. Toddy Drink: Traditional drink of Southern India made by fermenting sap from palms using natural yeast.

B. Microbes in Industrial Products (Alcohol & Antibiotics)

• Fermented Beverages: Brewer’s Yeast (Saccharomyces cerevisiae) ferments malted cereals and fruit juices to ethanol.

  • Non-Distilled (Lower alcohol concentration $<13\%$): Wine, Beer.

  • Distilled (Higher alcohol concentration): Whisky, Brandy, Rum, Vodka, Gin.

• Antibiotics (“Against Life”): Chemical substances produced by some microbes that kill or retard growth of other disease-causing microbes.

  • Discovery: Alexander Fleming chance discovery from fungus Penicillium notatum inhibiting bacterium Staphylococcus.

  • Full potential established by Ernest Chain and Howard Florey (used to treat wounded American soldiers in World War II; Nobel Prize awarded in 1945 to Fleming, Chain, and Florey).

  • Used to treat deadly diseases: Plague, Whooping cough (Kali khansi), Diphtheria (Gal ghotu), Leprosy (Kusht rog).

2. Chemicals, Enzymes, Bioactive Molecules & Sewage Treatment

A. Organic Acids, Enzymes & Bioactive Molecules

B. Microbes in Sewage Treatment Plant (STP)

• 1. Primary Treatment (Physical Stage): Physical removal of large & small particles.

  • Sequential Filtration: Removes floating debris.

  • Sedimentation: Removes grit (soil and small pebbles). Settled solids form Primary Sludge, supernatant forms Primary Effluent.

• 2. Secondary / Biological Treatment:

  • Primary effluent passed into large Aeration Tanks and constantly agitated $\to$ Allows vigorous growth of aerobic microbes into Flocs (masses of bacteria associated with fungal filaments to form mesh-like structures).

  • Flocs consume organic matter, significantly reducing Biochemical Oxygen Demand (BOD).

  • BOD Definition: Amount of oxygen required by aerobic microbes to oxidize organic matter in 1 litre of water. Higher BOD = More Polluted Water.

  • Once BOD is reduced, effluent passed into Settling Tank where flocs settle down as Activated Sludge.

  ↳ Small part used as inoculum for aeration tank.

  ↳ Major part pumped into Anaerobic Sludge Digesters containing anaerobic Methanogens $\to$ Digestion produces Biogas ($\text{CH}_4, \text{H}_2\text{S}, \text{CO}_2$).

3. Biogas Production & Biocontrol Agents

A. Microbes in Biogas Production

• Biogas: Mixture of gases (predominantly Methane $\text{CH}_4$, along with $\text{CO}_2, \text{H}_2, \text{H}_2\text{S}$) produced by anaerobic breakdown of cellulosic plant waste.
• Methanogens (e.g., Methanobacterium): Anaerobic bacteria growing on cellulosic material. Abundant in anaerobic sludge digesters and Rumen of cattle (helps in cellulose digestion; present in dung/gobar).
• Biogas Plant Layout:

  • Concrete tank ($10\text{–}15\text{ feet deep}$) fed with slurry of dung and bio-waste.

  • Floating cover rises as gas is generated by microbial activity.

  • Outlet pipe supplies gas to nearby houses for cooking & lighting; spent slurry removed as bio-fertilizer.

  • Developed in India by IARI (Indian Agricultural Research Institute) and KVIC (Khadi and Village Industries Commission).

B. Microbes as Biocontrol Agents

Natural biological methods for controlling plant diseases and pests without toxic chemical pesticides: