🦠 Microbes in Human Welfare
Microbes in Human Welfare
Microorganisms — bacteria, fungi, algae, and viruses — are often associated with disease. However, the vast majority of microbes are either harmless or actively beneficial to humans. This lesson explores the many ways microbes contribute to food production, medicine, agriculture, industry, energy generation, and waste management.
Microbes in Dairy Products
Curd and Yogurt
The transformation of milk into curd is one of the oldest and most familiar examples of microbial activity in daily life.
- Lactobacillus (a type of Lactic Acid Bacteria — LAB) converts the milk sugar lactose into lactic acid through fermentation
- The lactic acid lowers the pH, causing the main milk protein (casein) to coagulate (clump together), forming curd
- LAB also provide additional health benefits:
- Increases the vitamin B₁₂ content of curd compared to plain milk
- Checks the growth of disease-causing microbes in the stomach (acts as a natural probiotic)
- Yogurt is a more refined version of curd, produced using specific bacterial strains: Lactobacillus bulgaricus + Streptococcus thermophilus working together in a symbiotic culture
TIP
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Microbes in Human Welfare
Microorganisms — bacteria, fungi, algae, and viruses — are often associated with disease. However, the vast majority of microbes are either harmless or actively beneficial to humans. This lesson explores the many ways microbes contribute to food production, medicine, agriculture, industry, energy generation, and waste management.
Microbes in Dairy Products
Curd and Yogurt
The transformation of milk into curd is one of the oldest and most familiar examples of microbial activity in daily life.
- Lactobacillus (a type of Lactic Acid Bacteria — LAB) converts the milk sugar lactose into lactic acid through fermentation
- The lactic acid lowers the pH, causing the main milk protein (casein) to coagulate (clump together), forming curd
- LAB also provide additional health benefits:
- Increases the vitamin B₁₂ content of curd compared to plain milk
- Checks the growth of disease-causing microbes in the stomach (acts as a natural probiotic)
- Yogurt is a more refined version of curd, produced using specific bacterial strains: Lactobacillus bulgaricus + Streptococcus thermophilus working together in a symbiotic culture
TIP
This is why a small amount of curd (called an inoculum or "starter") is added to warm milk to make fresh curd — the Lactobacillus bacteria in the starter multiply and convert the entire batch of milk.
Cheese
Different types of cheese are produced using different microorganisms, and the specific microbe used determines the texture, flavor, and appearance of the final product:
| Type | Texture | Microorganism | Examples |
|---|---|---|---|
| Soft cheese | Soft, spreadable | Streptococcus spp. | Cottage cheese, cream cheese |
| Semi-hard cheese | Firm but flexible | Lactobacillus spp. | Cheddar, Gouda |
| Hard cheese | Very firm, aged | Propionibacterium shermanii (produces CO₂ gas during fermentation → the gas bubbles create the characteristic holes) | Swiss cheese (Emmental) |
| Ripened cheese | Soft, strong flavour | Penicillium roqueforti / P. camemberti (these fungi grow within the cheese during aging, producing distinctive blue-green veins and pungent flavor) | Roquefort, Camembert |
Toddy
- A traditional alcoholic drink made from palm sap (collected from coconut, palmyra, or date palm trees)
- Fermented naturally by wild yeasts present on the palm surface — no artificial inoculation is needed
- Contains approximately 4–5% alcohol
Microbes in Alcoholic Beverages
All alcoholic beverages are produced through fermentation — the anaerobic conversion of sugars to ethanol and carbon dioxide by yeast (Saccharomyces cerevisiae).
Ethanol fermentation equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (catalyzed by the enzyme zymase from yeast)
| Beverage | Raw Material | Alcohol Content | Notes |
|---|---|---|---|
| Beer | Barley malt (malted grain) | 3–6% | Brewed (not distilled); hops added for bitter flavour and preservation |
| Wine | Grape juice | 10–20% | Fermented only; types include red, white, and rosé |
| Brandy | Wine (distilled) | 60–70% | Essentially distilled wine — the alcohol is concentrated by heating |
| Whisky | Grain (barley, rye, corn) | 60–70% | Fermented + distilled; aged in oak barrels for flavor |
| Rum | Sugarcane molasses | ~40% | Fermented + distilled |
| Gin | Grain | ~40% | Distilled + flavoured with juniper berries |
| Vodka | Grain / potato | 40–50% | Distilled; a neutral spirit with minimal flavor |
NOTE
The key distinction: Brewing = fermentation only (produces beer, wine — lower alcohol content). Distillation = fermentation followed by heating to evaporate and recondense the alcohol, increasing its concentration (produces spirits like whisky, rum, brandy — higher alcohol content).
Microbes in Antibiotic Production
Antibiotics are chemical substances produced by microorganisms that can kill or inhibit the growth of other microorganisms. They are among the most important medical discoveries in human history.
Discovery of Antibiotics
- Alexander Fleming (1928) — discovered penicillin from the mould Penicillium notatum. He observed that a contaminating mould on a bacterial culture plate had created a zone of inhibition — an area where Staphylococcus bacteria could not grow. This accidental discovery launched the antibiotic era.
- Selman Waksman (1942) — coined the term "antibiotic" (meaning "against life")
- Fleming, Howard Florey, and Ernst Chain — received the Nobel Prize in 1945 for the development of penicillin as a practical medicine (Florey and Chain developed methods to mass-produce penicillin)
Important Antibiotics
| Antibiotic | Source Microorganism | Target |
|---|---|---|
| Penicillin | Penicillium notatum / P. chrysogenum | Gram-positive bacteria (inhibits cell wall synthesis) |
| Streptomycin | Streptomyces griseus | TB (Mycobacterium tuberculosis); Gram-negative bacteria |
| Tetracycline | Streptomyces aureofaciens | Broad-spectrum (effective against both Gram-positive and Gram-negative bacteria) |
| Chloramphenicol | Streptomyces venezuelae | Broad-spectrum; especially effective against typhoid |
| Erythromycin | Streptomyces erythreus | Alternative to penicillin for penicillin-allergic patients |
| Neomycin | Streptomyces fradiae | Topical antibiotic (applied on skin for surface infections) |
IMPORTANT
Most antibiotics are produced by Streptomyces species — these are actinomycetes (filamentous bacteria that grow like fungi). Streptomyces is the single most important genus in antibiotic production.
Microbes in Industrial Production
Organic Acids
Microbes are used as living factories to produce organic acids at industrial scale — these are cheaper and more sustainable than chemical synthesis:
| Organic Acid | Microorganism | Application |
|---|---|---|
| Citric acid | Aspergillus niger (fungus) | Food industry (preservative, flavouring agent in soft drinks), pharmaceuticals |
| Acetic acid (vinegar) | Acetobacter aceti (bacterium) | Food (vinegar production), chemical industry |
| Lactic acid | Lactobacillus bulgaricus (bacterium) | Food processing, pharmaceuticals, biodegradable plastics (PLA) |
| Butyric acid | Clostridium butylicum (bacterium) | Chemical industry |
| Gluconic acid | Aspergillus niger | Pharmaceuticals (calcium gluconate supplements) |
| Oxalic acid | Aspergillus niger | Textile and leather industry |
Enzymes
Microbial enzymes are widely used in industry because they are highly efficient, specific, and can be produced in large quantities:
| Enzyme | Source | Application |
|---|---|---|
| Pectinase | Aspergillus niger | Clarification of fruit juices — breaks down pectin (the substance that makes juice cloudy) to produce clear juice |
| Protease | Bacillus spp. | Detergent industry (removes protein stains like blood, egg); leather processing |
| Lipase | Various fungi/bacteria | Detergent industry (removes fat/oil stains) |
| Amylase | Aspergillus / Bacillus | Starch processing; brewing; baking (breaks down starch into sugars) |
| Streptokinase | Streptococcus | Clot buster — dissolves blood clots in heart attack patients (thrombolytic agent); a life-saving medical enzyme |
| Cellulase | Trichoderma | Textile industry (bio-polishing of fabrics); biofuel production (breaks down cellulose into fermentable sugars) |
Important Bioactive Molecules
| Product | Source | Application |
|---|---|---|
| Cyclosporin A | Trichoderma polysporum (fungus) | Immunosuppressant — used in organ transplantation to prevent the immune system from rejecting the transplanted organ |
| Statins | Monascus purpureus (yeast) | Cholesterol-lowering agent — works by inhibiting HMG-CoA reductase, the key enzyme in the cholesterol synthesis pathway. Statins are among the most prescribed drugs worldwide. |
Microbes as Biopesticides
Biopesticides are biological agents used to control agricultural pests. They are environmentally friendly alternatives to chemical pesticides.
Bacillus thuringiensis (Bt)
- A Gram-positive soil bacterium that has become one of the most important biopesticides globally
- Produces crystal proteins (Cry proteins) during sporulation (spore formation)
- Cry proteins are specifically toxic to insect larvae, especially Lepidoptera (caterpillars/moth larvae)
- Mechanism of action: Cry protein is ingested by the insect larva → dissolved in the alkaline insect gut (pH ~9–10) → binds to specific receptors on gut epithelial cells → creates pores in the cell membrane → gut lysis (destruction) → insect death
- Cry genes (such as cry1Ac, cry2Ab) have been transferred to crop plants through genetic engineering → creating Bt crops (Bt cotton, Bt brinjal) that produce their own insecticide
- Bt toxin is highly specific to target insects and is safe for humans, animals, and beneficial insects — the toxin is only activated in the alkaline gut of susceptible insects (human stomachs are acidic)
Nuclear Polyhedrosis Virus (NPV)
- A baculovirus that specifically infects insect pests (especially Lepidoptera, Hymenoptera, Coleoptera)
- Highly species-specific → does not harm beneficial insects, plants, animals, or humans
- Environmentally safe biological control agent
- The virus multiplies inside insect cells → kills the insect from within
Trichoderma (as Biocontrol Agent)
- A free-living fungus commonly found in the root ecosystem (rhizosphere)
- Provides biological control of several plant pathogens (especially soil-borne fungi)
- Mechanism: mycoparasitism (directly attacks and parasitizes other fungi), competition (outcompetes pathogens for space and nutrients), antibiosis (produces antimicrobial compounds)
- Also produces cellulase and other industrially useful enzymes
Microbes as Biofertilizers
Biofertilizers are microorganisms that enrich the soil with essential nutrients, reducing or replacing the need for chemical fertilizers. They are key to sustainable agriculture.
| Biofertilizer | Type | Function |
|---|---|---|
| Rhizobium | Bacterium (symbiotic) | Fixes atmospheric N₂ in root nodules of legumes through a mutualistic relationship; converts N₂ → NH₃ using the enzyme nitrogenase. This is why legumes (pulses) are rotated with cereal crops — they naturally enrich the soil with nitrogen. |
| Azotobacter | Bacterium (free-living) | Free-living nitrogen fixer in soil; does not require a plant partner |
| Azospirillum | Bacterium (associative) | Associates with the roots of grasses (wheat, maize, rice); fixes nitrogen in the rhizosphere |
| Cyanobacteria (e.g., Anabaena, Nostoc) | Photosynthetic bacteria | Fix nitrogen using heterocysts (specialized thick-walled cells); especially important in paddy fields (rice cultivation) where standing water supports their growth |
| Azolla | Aquatic fern | Contains Anabaena azollae (a cyanobacterium) living symbiotically in its leaf cavities; used as green manure in rice fields; fixes 40–60 kg N/ha/year |
| Mycorrhiza | Fungus (symbiotic) | Fungal association with plant roots; greatly enhances phosphorus absorption (the fungal hyphae extend far beyond the root system, accessing phosphorus from a much larger soil volume); also absorbs water and other minerals. Two types: ectomycorrhiza (fungus on root surface) and endomycorrhiza / VAM (fungus penetrates within root cells) |
| Phosphate-solubilizing bacteria | Bacillus, Pseudomonas | Convert insoluble phosphate in soil to soluble form that plants can absorb — makes locked-up soil phosphorus available |
IMPORTANT
For exams, remember: Rhizobium = nitrogen fixation in legume root nodules. Mycorrhiza = phosphorus absorption. Azolla + Anabaena = green manure in rice fields. These three are the most frequently tested biofertilizers.
Single Cell Protein (SCP)
SCP (Single Cell Protein) is protein-rich biomass produced by growing microorganisms on industrial scale. It offers a solution to global protein shortage because microbes multiply exponentially and can be grown on waste substrates.
| Microorganism | Feature |
|---|---|
| Spirulina | Cyanobacterium; contains ~65% protein (one of the highest protein contents of any food); can be grown on wastewater; rich in vitamins (B₁₂, beta-carotene) and minerals |
| Methylophilus methylotrophus | Bacterium; grown on methanol (a cheap industrial chemical); ICI's "Pruteen" product (used as animal feed) |
| Saccharomyces cerevisiae | Yeast; traditional SCP source |
| Candida utilis | Yeast; known as "Torula" yeast; used as food supplement |
Efficiency Comparison
The efficiency advantage of microbial protein production over conventional animal farming is staggering:
| Source | Biomass | Daily Protein Production |
|---|---|---|
| 250 kg cow | Large animal | ~200 g protein/day |
| 250 kg microbial biomass (Methylophilus) | Same weight | ~25 tonnes protein/day (through rapid multiplication) |
NOTE
Microbes can double their biomass in 20–120 minutes compared to months or years for animals. This exponential growth rate makes them extraordinarily efficient protein factories — the same starting mass of microbes produces roughly 125,000 times more protein daily than a cow of the same weight.
Bioethanol
Bioethanol (C₂H₅OH) is ethanol produced through the fermentation of plant-derived biomass. It is a renewable fuel that can partially replace petroleum-based petrol.
- Produced by yeast (Saccharomyces cerevisiae) fermentation of sugars
- Primary feedstock: sugarcane (molasses), corn, wheat, cellulosic biomass
| Feature | Details |
|---|---|
| Chemical formula | C₂H₅OH |
| Feedstock | Sugarcane (Brazil), corn (USA), molasses (India) |
| Brazil model | World leader in bioethanol production; sugarcane-based; "flex-fuel" vehicles can run on any blend of petrol and ethanol |
| India | Government target of 5–20% ethanol blending with petrol (E5 to E20 program) |
| Advantages | Renewable; reduces CO₂ emissions (carbon-neutral cycle); reduces dependence on fossil fuels |
| Limitation | Competition with food crops for land; may drive up food prices; water-intensive production |
Biogas
Biogas is a mixture of gases (primarily methane) produced by the anaerobic digestion (breakdown in the absence of oxygen) of organic waste such as cow dung, agricultural residues, and sewage.
Three Stages of Biogas Production
Biogas production is a sequential process involving three different groups of microorganisms:
| Stage | Microorganisms | Process |
|---|---|---|
| 1. Hydrolysis | Facultative anaerobes (e.g., Clostridium) | Complex organic matter (carbohydrates, proteins, fats) broken down into simple sugars, amino acids, and fatty acids |
| 2. Acidogenesis | Acidogenic bacteria | Simple molecules converted into organic acids (acetic, propionic, butyric acid) + CO₂ + H₂ |
| 3. Methanogenesis | Methanogenic archaea (e.g., Methanobacterium, Methanococcus) | Organic acids converted into methane (CH₄) + CO₂. These methanogens are archaea (not bacteria) and are strict anaerobes — they die in the presence of oxygen. |
Rate-limiting step: Cellulose hydrolysis — the breakdown of cellulose is the slowest step in the entire process, determining the overall speed of biogas production.
Biogas Composition
| Component | Percentage |
|---|---|
| Methane (CH₄) | 50–70% (this is the combustible component that gives biogas its fuel value) |
| Carbon dioxide (CO₂) | 30–40% |
| Hydrogen sulfide (H₂S) | Trace (gives biogas its characteristic odor) |
| Nitrogen, hydrogen | Trace |
KVIC Gobar Gas Plants
- KVIC = Khadi and Village Industries Commission — the Indian government body that promoted biogas technology in rural areas
- Promoted gobar gas (biogas) plants using cow dung as the primary feedstock
- Two main designs: floating dome (KVIC model — steel gas holder floats on slurry) and fixed dome (Janata model — gas collects under a fixed concrete dome)
- Input: cow dung (gobar) + water → mixed into slurry
- Output: biogas (used for cooking, lighting, and electricity generation) + spent slurry (an excellent organic fertilizer rich in nitrogen, phosphorus, and potassium)
- Benefits: provides clean fuel, reduces deforestation (less need for firewood), manages agricultural waste, produces free fertilizer
Microbes in Sewage Treatment
Untreated sewage is a major source of water pollution. Sewage treatment uses microbes to break down organic waste and make the water safe for release into the environment. The process occurs in stages:
Primary Treatment (Physical)
- Physical processes: filtration and sedimentation to remove large debris (rags, sticks, stones) and suspended solids
- Primary sludge (heavy organic solids) settles at the bottom of sedimentation tanks
- This stage removes ~50–60% of suspended solids but does not significantly reduce dissolved organic matter
Secondary Treatment (Biological)
This is where microbes play the central role:
- Aeration tanks: the effluent from primary treatment is mixed with aerobic bacteria and vigorously aerated (pumped with air)
- This is called the activated sludge process — bacteria consume and decompose the dissolved organic matter
- The key measure of treatment success is the reduction of BOD (Biochemical Oxygen Demand):
- BOD = the amount of oxygen required by microbes to decompose organic matter in water
- High BOD = heavily polluted water (lots of organic waste consuming oxygen)
- Low BOD = clean water (little organic waste)
- After aeration, the effluent passes through settling tanks where activated sludge (bacterial flocs — clumps of bacteria) settles to the bottom
- A portion of the settled sludge is recycled back to the aeration tank as an inoculum (to maintain the bacterial population); the rest goes to the anaerobic sludge digester
Anaerobic Sludge Digester
- Anaerobic bacteria decompose the remaining sludge in the absence of oxygen
- This produces biogas (methane + CO₂), which can be used as fuel — turning a waste treatment process into an energy source
- The remaining solid material is dried and can be used as fertilizer or disposed of safely
TIP
The sewage treatment process essentially mimics what happens naturally in rivers and lakes — but at a much faster rate and in a controlled environment. The key difference is aeration — by pumping air into the treatment tanks, we greatly accelerate the microbial decomposition process.
Beginner's Box — Practice Questions
Set 1: Fermented Foods and Beverages
-
Which microorganism is used in curd making? Answer: Lactobacillus (Lactic Acid Bacteria)
-
The holes in Swiss cheese are produced by: Answer: Propionibacterium shermanii (produces CO₂ gas)
-
Roquefort cheese is ripened using: Answer: Penicillium roqueforti
-
Alcohol content in beer is approximately: Answer: 3–6%
-
The yeast used in alcoholic fermentation is: Answer: Saccharomyces cerevisiae
Set 2: Antibiotics and Industrial Products
-
Who coined the term "antibiotic"? Answer: Selman Waksman (1942)
-
Penicillin was discovered by: Answer: Alexander Fleming (1928)
-
Citric acid is commercially produced using: Answer: Aspergillus niger
-
Streptokinase (clot buster) is obtained from: Answer: Streptococcus
-
Cyclosporin A is used as: Answer: Immunosuppressant (in organ transplantation)
Set 3: Biopesticides and Biofertilizers
-
Bt toxin is produced by: Answer: Bacillus thuringiensis
-
Cry proteins are toxic to which group of insects primarily? Answer: Lepidoptera (moth/butterfly larvae — caterpillars)
-
Rhizobium fixes nitrogen in association with: Answer: Leguminous plants (in root nodules)
-
Mycorrhiza primarily helps in absorption of: Answer: Phosphorus
-
Azolla is used as green manure in: Answer: Rice (paddy) fields
Set 4: SCP, Bioethanol, Biogas
-
Spirulina contains approximately what percentage protein? Answer: ~65%
-
The primary feedstock for bioethanol in Brazil is: Answer: Sugarcane
-
The methane content in biogas is approximately: Answer: 50–70%
-
The rate-limiting step in biogas production is: Answer: Cellulose hydrolysis (breakdown)
-
KVIC stands for: Answer: Khadi and Village Industries Commission
Image Generation Prompts
Image Generation Prompt 1: Biogas Plant Diagram — Floating Dome Type
A detailed cross-sectional diagram of a floating dome (KVIC model) biogas plant. Show the main components: (1) Inlet/mixing tank on one side where cow dung and water are mixed into slurry; (2) Underground cylindrical digester tank (made of brick/concrete) where anaerobic digestion occurs — label the three zones inside: acidogenesis zone (top), active digestion zone (middle with bacteria illustrated), and sludge zone (bottom); (3) Floating gas holder dome (inverted steel drum) sitting on top of the slurry inside the digester, rising as gas accumulates; (4) Gas outlet pipe from the top of the dome leading to a stove/burner; (5) Outlet/overflow tank on the opposite side where spent slurry (used as fertilizer) exits. Label the three stages of biogas production: hydrolysis (complex organics to simple molecules), acidogenesis (simple molecules to organic acids), and methanogenesis (organic acids to methane by Methanobacterium). Show biogas composition annotation: 50-70% CH4, 30-40% CO2. Clean engineering diagram style with cross-hatching for soil and concrete.
Image Generation Prompt 2: Fermentation Process Flowchart
A flowchart-style diagram showing the ethanol fermentation process by yeast (Saccharomyces cerevisiae). Start with raw materials at the top branching into three paths: sugarcane molasses, grain (barley malt), and grape juice. Show the common process: raw material undergoes pre-treatment (milling, mashing for grains; crushing for grapes), then enters the fermentation vessel (large tank with yeast cells illustrated inside). Show the chemical equation prominently: C6H12O6 → 2C2H5OH + 2CO2 (catalyzed by zymase enzyme from yeast). From the fermentation tank, show two output paths: (1) Brewed products (beer 3-6%, wine 10-20%) directly from fermentation; (2) Distilled products through a distillation column (whisky, rum, brandy at 40-70% alcohol). Label temperature conditions (25-30 degrees C) and anaerobic conditions. Include a small inset of yeast cells budding. Clean process engineering flowchart style with arrows and labeled boxes.
Image Generation Prompt 3: Penicillium Mold Colony Producing Penicillin
An educational illustration showing how Penicillium notatum produces penicillin. Show a Petri dish view (from above) with a Penicillium mold colony (blue-green fuzzy circular growth) in the center, surrounded by a clear zone of inhibition where bacterial growth (Staphylococcus colonies, shown as small dots) is absent. Around the clear zone, show normal bacterial colonies growing. Include an enlarged inset of the Penicillium conidiophore structure: show the branching hyphae, metulae, phialides, and chains of conidia (spores) at the tips, with penicillin molecules being secreted into the surrounding medium (shown as small triangular shapes diffusing outward). Add a text annotation: "Alexander Fleming, 1928" and "Penicillin inhibits bacterial cell wall synthesis." Clean microbiology textbook illustration style.
Image Generation Prompt 4: Biological Nitrogen Fixation in Root Nodule
A detailed cross-sectional diagram of a legume root nodule showing the process of biological nitrogen fixation by Rhizobium. Show the overall root with a visible nodule (swelling) on the surface. In the cross-section of the nodule, label: outer cortex, vascular bundles connecting to root vasculature, and the central infected zone containing bacteroid-filled cells. Show an enlarged inset of a single infected cell containing bacteroids (rod-shaped Rhizobium cells inside peribacteroid membrane/symbiosome). Illustrate the biochemical process: atmospheric N2 entering through intercellular spaces, the nitrogenase enzyme complex (inside bacteroids) converting N2 + 8H+ + 8e- + 16ATP → 2NH3 + H2 + 16ADP. Show leghemoglobin (pink-colored oxygen-binding protein) in the nodule maintaining low O2 for nitrogenase function. Show NH3 being converted to amino acids and exported to the plant via xylem. Label the root hair infection thread where Rhizobium initially enters. Clean plant biology textbook style with color coding.
Summary Cheat Sheet
| Concept / Topic | Key Details / Explanation |
|---|---|
| Dairy Products | Curd: Lactobacillus (LAB) converts lactose → lactic acid → casein coagulates Yogurt: specific Lactobacillus bulgaricus + Streptococcus thermophilus Swiss cheese: Propionibacterium shermanii (produces CO₂ → holes) Roquefort cheese: ripened by Penicillium roqueforti |
| Alcoholic Beverages | Yeast: Saccharomyces cerevisiae (brewer's yeast) Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (by zymase enzyme) Beer: 3–6% alcohol (from barley malt) Wine: 10–20% (from grape juice) Distilled spirits (whisky, rum, brandy): 40–70% (distillation after fermentation) |
| Antibiotics | Alexander Fleming (1928): discovered penicillin from Penicillium notatum Selman Waksman (1942): coined the term "antibiotic" Ernest Chain & Howard Florey: mass-produced penicillin Penicillin inhibits bacterial cell wall synthesis |
| Industrial Products — Organic Acids | Citric acid: Aspergillus niger Acetic acid: Acetobacter aceti Butyric acid: Clostridium butylicum Lactic acid: Lactobacillus |
| Industrial Products — Enzymes | Lipases: used in laundry detergents (remove oil/grease stains) Pectinases + Proteases: clarify fruit juices Streptokinase: from Streptococcus, used as clot buster (thrombolytic) Amylases: starch processing |
| Bioactive Molecules | Cyclosporin A: from Trichoderma polysporum, used as immunosuppressant (organ transplants) Statins: from Monascus purpureus, lower blood cholesterol (inhibit HMG-CoA reductase) |
| Biopesticides — Bt (Bacillus thuringiensis) | Produces Cry proteins (crystal proteins) as protoxins (inactive) In insect gut (alkaline pH): protoxin → active Bt toxin → binds to midgut epithelium → creates pores → insect death Cry1Ac, Cry2Ab: toxic to Lepidoptera (cotton bollworm) → Bt cotton Cry3Bb: toxic to Coleoptera (beetles) Cry4: toxic to Diptera (mosquitoes) |
| Biopesticides — Others | NPV (Nucleopolyhedrovirus): kills specific insect pests (narrow host range), safe for non-target organisms Trichoderma: fungal biocontrol agent against soil-borne plant pathogens |
| Biofertilizers | Rhizobium: fixes N₂ in root nodules of legumes (symbiotic) Azotobacter: free-living N₂ fixer (in soil) Azospirillum: associative N₂ fixer (in rhizosphere of grasses, cereals) Cyanobacteria (Anabaena, Nostoc): fix N₂ in paddy fields using heterocysts Azolla: aquatic fern with symbiotic Anabaena azollae → green manure in rice fields Mycorrhiza (VAM): fungus-root association, helps absorb phosphorus |
| SCP (Single Cell Protein) | Microbial biomass used as protein-rich food/feed Spirulina: ~65% protein, grown on wastewater Methylophilus methylotrophus: grown on methanol (ICI "Pruteen" process) |
| Bioethanol | 1st generation: from sugar/starch crops — sugarcane (Brazil), corn (USA) 2nd generation: from cellulosic biomass (agricultural waste) E10 blend: 10% ethanol + 90% petrol |
| Biogas | Produced by anaerobic digestion of organic waste Composition: 50–70% CH₄ (methane) + 30–40% CO₂ Key organism: Methanobacterium (methanogenic archaebacterium) KVIC model: floating dome type biogas plant 3 stages: hydrolysis → acidogenesis → methanogenesis (rate-limiting step: cellulose hydrolysis) |
| Sewage Treatment | Primary treatment: physical (screening, sedimentation) → removes large debris + suspended solids Secondary treatment: biological — aeration tank (aerobic bacteria decompose organic matter), measured by BOD (Biochemical Oxygen Demand) High BOD = heavily polluted; Low BOD = clean water Activated sludge: bacterial flocs recycled as inoculum Anaerobic sludge digester: produces biogas (methane) |
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