Microbes in Human Welfare

MICROBES IN HUMAN WELFARE

Microbes (bacteria, fungi, protozoa, viruses, viroids, and prions) are ubiquitous organisms found in soil, water, air, and inside living bodies. While many microbes cause diseases, numerous microbes are extremely beneficial to human welfare through diverse applications in food production, industrial synthesis, environmental treatment, and agriculture.

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MICROBES IN HOUSEHOLD PRODUCTS

Lactic Acid Fermentation and Curd Production

**Lactobacillus** and other **lactic acid bacteria (LAB)** are used commercially to convert milk into curd. During fermentation:

LAB metabolize lactose through anaerobic respiration (fermentation pathway), producing **lactic acid** as an end product

Lactic acid lowers the pH of milk, causing **coagulation and partial digestion of milk proteins** (casein)

A small inoculum (starter culture) containing millions of LAB cells is added to fresh milk

Under optimal temperature conditions (around 40-45°C), LAB multiply rapidly, converting milk to curd

**Nutritional enhancement**: LAB synthesize **Vitamin B₁₂** during fermentation, increasing the nutritional quality of curd

LAB in the stomach and intestinal tract help prevent growth of disease-causing pathogens through **competitive exclusion** and production of antimicrobial compounds

Fermented Dough and Bread

**Dosa and Idli**: Traditional fermented foods prepared from dough

Natural bacteria and fungi in the dough ferment carbohydrates

Anaerobic conditions lead to **CO₂ production** (through heterolactic fermentation), causing the characteristic **puffed-up appearance**

Sources of bacteria: naturally present in flour, utensils, and environment

**Bread Making**: Baker's yeast (**Saccharomyces cerevisiae**) is used to ferment bread dough

Yeast performs **alcoholic fermentation**, producing CO₂ gas and ethanol

CO₂ gas makes the dough rise (leavening action)

Ethanol evaporates during baking, leaving the characteristic bread texture

Different strains of yeast produce different flavor profiles

Fermented Beverages and Drinks

**Toddy**: Traditional southern Indian fermented drink made from palm sap

Naturally occurring microbes ferment the sap

Produces characteristic flavor and mild alcoholic content

**Fish, Soybean, and Bamboo Shoot Fermentation**: Various microbes ferment these foods, producing characteristic tastes and improving digestibility

Cheese Production

Different varieties of cheese are produced using **specific microbes**, resulting in unique textures, flavors, and tastes:

**Swiss Cheese**: Large holes are produced by **Propionibacterium sharmanii**, which generates large amounts of **CO₂** during anaerobic fermentation

**Roquefort Cheese**: A specific **fungus** is grown on cheese during ripening, producing the characteristic blue veining and distinctive flavor through enzymatic breakdown of proteins and fats

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MICROBES IN INDUSTRIAL PRODUCTS

Fermented Beverages

**Yeast Species**: **Saccharomyces cerevisiae** (brewer's yeast or baker's yeast) is used industrially for fermentation

**Production Process**:

**Substrate**: Malted cereals or fruit juices containing sugars (glucose, fructose)

**Metabolic Pathway**: Alcoholic fermentation under anaerobic conditions

Glucose → 2 Pyruvate (glycolysis)

Pyruvate → Ethanol + CO₂ (anaerobic respiration)

**Fermentation Vessels**: Large fermentors (10,000-100,000 liters) with temperature and pH control systems

**Types of Beverages**:

**Wine and Beer**: Produced **without distillation**; contain lower alcohol content (5-15%)

**Whisky, Brandy, and Rum**: Produced by **distillation** of fermented broth; contain higher alcohol content (40-60%)

**Variables Affecting Product Type**: Raw material used, fermentation temperature, duration, processing method (with/without distillation), and microbial strain selection

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Antibiotics

**Definition**: Chemical substances produced by microbes that **kill or retard the growth of disease-causing microorganisms** (pathogens) while being beneficial to human health

**Historical Discovery**:

**Alexander Fleming** (1928) discovered Penicillin by chance while studying *Staphylococci* bacteria

Observed mold contamination on an unwashed culture plate where bacteria could not grow

Identified the mold as **Penicillium notatum**, which produced an antimicrobial chemical

**Ernest Chain** and **Howard Florey** later established Penicillin's full clinical potential

Used extensively to treat wounded soldiers in World War II

Fleming, Chain, and Florey awarded the Nobel Prize in 1945

**Penicillin Mechanism**:

Inhibits bacterial cell wall synthesis

Causes cell lysis and death in bacteria

Selective toxicity: affects bacteria but not mammalian cells (which lack cell walls)

**Other Antibiotic Sources**:

**Streptomyces species**: Produce streptomycin, tetracycline, chloramphenicol

**Bacillus species**: Produce bacitracin

**Cephalosporium species**: Produce cephalosporins

**Clinical Significance**: Antibiotics revolutionized treatment of previously fatal bacterial diseases including **plague, whooping cough (pertussis), diphtheria, and leprosy**, saving millions of lives globally

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Chemicals, Enzymes, and Bioactive Molecules

**Organic Acids Production**:

| Acid | Microbial Producer | Industrial Use |

|------|-------------------|---|

| Citric Acid | **Aspergillus niger** (fungus) | Food preservation, beverages, pH regulation |

| Acetic Acid | **Acetobacter aceti** (bacterium) | Vinegar production, food preservation |

| Butyric Acid | **Clostridium butylicum** (bacterium) | Flavoring, pharmaceutical compounds |

| Lactic Acid | **Lactobacillus** species | Food preservation, industrial chemical |

**Ethanol Production**: **Saccharomyces cerevisiae** used for large-scale ethanol fermentation (biofuel production, industrial solvent)

**Enzyme Production and Applications**:

**Lipases**:

Produced by microbes and incorporated into detergent formulations

Function: Break down oily and fatty stains on textiles

Mechanism: Enzymatic hydrolysis of ester bonds in lipids

**Pectinases and Proteases**:

Used for clarification of bottled fruit juices

Commercial juices are clearer than homemade juice because these enzymes break down pectin (polysaccharide) and proteins

Results in improved transparency and shelf stability

**Streptokinase**:

Produced by **Streptococcus** bacteria

Modified through **genetic engineering**

Function: Acts as a **clot buster** (thrombolytic agent)

Clinical Use: Administered to patients with **myocardial infarction (heart attack)** to dissolve blood clots in coronary arteries

Restores blood flow and prevents tissue necrosis

**Cyclosporin A**:

Produced by fungus **Trichoderma polysporum**

Function: **Immunosuppressive agent**

Clinical Use: Prevents organ rejection in transplant patients by suppressing T-lymphocyte activation

**Statins** (Blood-Cholesterol Lowering Agents):

Produced by yeast **Monascus purpureus**

Mechanism: **Competitively inhibit HMG-CoA reductase**, the enzyme catalyzing the rate-limiting step of cholesterol synthesis

Clinical Use: Reduces blood LDL cholesterol levels, preventing atherosclerosis and cardiovascular disease

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MICROBES IN SEWAGE TREATMENT

**Sewage Definition**: Municipal waste water containing organic matter, water, and diverse microorganisms (many pathogenic) from domestic and industrial sources

**Problem**: Large quantities of sewage cannot be discharged directly into rivers and streams as it causes **water pollution** and increases **water-borne diseases** (cholera, typhoid, hepatitis A, dysentery)

**Solution**: Treatment in **Sewage Treatment Plants (STPs)** using microbial action before discharge into natural water bodies

Primary Treatment (Physical Treatment)

**Objective**: Mechanical removal of large and small suspended particles through physical separation

**Process Steps**:

1. **Sequential Filtration**: Floating debris (leaves, paper, plastic, wood) removed through mesh screens and coarse filters

2. **Sedimentation**: Grit (soil particles, small pebbles, sand) removed in **grit chambers** where heavy particles settle under gravity

3. **Collection**: All settled solids form the **primary sludge**

4. **Supernatant**: Clear liquid above the sludge becomes the **effluent** (partially treated water) passed to secondary treatment

**Output**: Primary effluent contains dissolved organic matter, bacteria, and nutrients requiring further biological treatment

Secondary Treatment (Biological/Aerobic Treatment)

**Objective**: Reduce **BOD (Biochemical Oxygen Demand)** through microbial oxidation of organic matter

**BOD Definition**: The amount of dissolved oxygen (in mg/L) consumed by aerobic microorganisms when oxidizing all organic matter in water over a standard period (typically 5 days at 20°C)

**Higher BOD** = Greater organic pollution and polluting potential

**Lower BOD** = Water suitable for discharge into natural water bodies

**Process Steps**:

1. **Aeration Stage**:

Primary effluent pumped into large **aeration tanks** (exposed to air)

**Mechanical agitation** (rotating paddles/aerators) and **continuous air pumping** create aerobic conditions

Oxygen dissolved in water supports aerobic bacterial growth

2. **Floc Formation**:

Beneficial aerobic heterotrophic bacteria multiply rapidly

Bacteria form **flocs**: masses of bacterial cells associated with **fungal filaments**, creating **mesh-like structures**

Examples: *Zooglea*, *Pseudomonas*, *Aspergillus*, and other fungi

3. **Organic Matter Degradation**:

Floc-forming microbes oxidize organic compounds (carbohydrates, proteins, fats)

Complete oxidation pathway: Organic matter + O₂ → CO₂ + H₂O + energy + microbial biomass

**Significant reduction in BOD** (70-90% removal)

Retention time in aeration tanks: **6-8 hours**

4. **Settling Stage**:

Effluent passed into **settling tanks** (secondary sedimentation tanks)

Bacterial flocs settle under gravity to tank bottom

Clear liquid (secondary effluent) decanted and discharged into natural water bodies

5. **Activated Sludge Management**:

Settled sediment called **activated sludge** (rich in microbes and organic matter)

**Small portion** (5-10%) recycled back to aeration tank as **inoculum** to maintain high microbial population

**Major portion** (90-95%) pumped to anaerobic digesters

Anaerobic Sludge Digestion

**Objective**: Further breakdown of remaining organic matter and microbial biomass; generate biogas energy

**Process**:

Activated sludge transferred to large **anaerobic sludge digesters** (sealed tanks with no oxygen)

**Anaerobic bacteria** (particularly **methanogens**) grow and digest sludge

Pathogenic organisms destroyed through competitive exclusion and anaerobic conditions

**Products**:

**Biogas mixture**: Predominantly **methane (CH₄)** with **hydrogen sulfide (H₂S)** and **carbon dioxide (CO₂)**

**Energy generation**: Biogas is **inflammable** and used as fuel for plant operations or nearby facilities

**Residual sludge**: Nutrient-rich material suitable for agriculture

**Advantages of Microbial Sewage Treatment**:

No toxic chemicals required

Sustainable and cost-effective

Proven methodology for over 100 years globally

No man-made technology rivals microbial treatment efficiency

Produces usable biogas as byproduct

**Current Challenges in India**:

Rapid urbanization produces more sewage than treatment capacity

**Ganga Action Plan** and **Yamuna Action Plan**: Government initiatives to build additional STPs and prevent direct untreated sewage discharge into major rivers

Objective: Reduce water pollution and water-borne disease incidence

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MICROBES IN PRODUCTION OF BIOGAS

**Biogas Definition**: Mixture of gases produced by microbial metabolism under anaerobic conditions, predominantly containing **methane (CH₄)**, used as fuel

**Methanogenic Bacteria**: Specialized anaerobic bacteria that produce large quantities of methane

**Key Methanogen**: **Methanobacterium** species

Grow exclusively under anaerobic conditions

Require cellulosic material (plant fiber) as substrate

Metabolic pathway: Cellulose + anaerobic metabolism → CH₄ + CO₂ + H₂

Natural Biogas Production Sites

**Anaerobic Sludge Digesters**: Methanogens naturally present produce biogas during sewage treatment

**Ruminant Digestive System** (especially cattle):

Large fermentation chamber in rumen (first stomach compartment)

Methanogens break down ingested cellulose

Cattle cannot digest cellulose; methanogens facilitate this process

**Cattle excreta (gobar/dung)** is rich in these methanogens

Function: Important for cattle nutrition through volatile fatty acid production

**Note**: Humans lack methanogens in digestive systems and cannot digest cellulose; dietary fiber passes undigested

Biogas Plant Technology

**Biogas plant**: Engineered system using cattle dung to generate methane gas for domestic energy

**Structure**:

**Concrete tank**: 10-15 feet deep (semi-underground to maintain temperature)

**Input**: Slurry of cattle dung mixed with water and bio-wastes

**Floating cover**: Sealed lid that rises as gas accumulates inside tank

**Outlets**:

**Gas outlet**: Connected to pipeline supplying biogas to nearby houses

**Sludge outlet**: Spent slurry (digested material) removed for use as fertilizer

**Operating Principle**:

Anaerobic conditions maintained in sealed tank

Methanogens and other anaerobic bacteria digest organic matter in dung

**Microbial metabolism** produces biogas continuously

Gas pressure builds up, rising the floating cover

Gas extracted and supplied through pipes

**Advantages**:

**Renewable energy source**: Continuous gas production from available cattle dung

**Waste management**: Converts animal waste into useful fuel

**Fertilizer byproduct**: Spent slurry is nutrient-rich manure for agriculture

**Rural applicability**: Cost-effective energy solution for village areas with cattle farming

**Environmental**: Reduces methane emissions that would otherwise escape to atmosphere; uses in biogas plant is controlled combustion

**Indian Development**: Biogas technology developed through efforts of:

**Indian Agricultural Research Institute (IARI)**

**Khadi and Village Industries Commission (KVIC)**

**Geographic Suitability**: Predominantly in rural areas where cattle rearing is common and cattle dung readily available

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MICROBES AS BIOCONTROL AGENTS

**Biocontrol Definition**: Use of **biological methods** (living organisms or their products) to control plant diseases, agricultural pests, and unwanted organisms instead of chemical insecticides and pesticides

Problems with Chemical Pesticides

**Toxicity**: Extremely harmful to humans, animals, and beneficial organisms

**Environmental pollution**: Contaminates soil, groundwater, surface water, fruits, vegetables, and crops

**Non-selectivity**: Kills both harmful pests and beneficial insects indiscriminately

**Persistence**: Chemicals remain in environment for extended periods

**Bioaccumulation**: Accumulate in food chains, magnifying concentration in higher trophic levels

Principles of Biological Pest Management

**Organic/Sustainable Farming Approach**:

**Biodiversity principle**: Higher diversity leads to greater ecosystem stability and sustainability

**Ecosystem balance**: Pests NOT completely eradicated, but maintained at manageable levels through natural predation and parasitism

**Complex food webs**: Understanding and encouraging natural predator-prey relationships

**Holistic approach**: Recognizing that pest organisms support beneficial predatory and parasitic insects that feed on them

**Reduced chemical dependence**: Biocontrol measures minimize reliance on toxic pesticides

Natural Predators of Common Agricultural Pests

| Pest | Natural Predator | Mechanism |

|------|---|---|

| Aphids | **Ladybird** beetle (red and black markings) | Predation; larvae and adults consume aphids |

| Mosquitoes | **Dragonflies** | Predation of mosquito larvae and adults |

| Plant-feeding insects | Various parasitic wasps | Parasitism; lay eggs in pest insects |

Bacterial Biocontrol: Bacillus thuringiensis (Bt)

**Organism**: Gram-positive, rod-shaped bacterium *Bacillus thuringiensis*

**Bt Toxin**:

Encodes **Cry proteins** (crystal proteins with insecticidal properties)

Different Cry proteins target specific insect orders (lepidopterans, coleopterans, dipterans)

**Cry1Ac** and **Cry2Aa**: Primarily active against butterfly and moth caterpillars (*Lepidoptera*)

**Commercial Application**:

Supplied as **dried spores** in sachets

Mixed with water to form suspension

Sprayed onto vulnerable crop plants (brassicas like cabbage, fruit trees, cotton)

**Mechanism of Action**:

1. Insect larvae consume plant material containing Bt spores

2. In larval **midgut** (alkaline pH ~7.5-8.5): Spore coat dissolves, releasing Cry protein crystals

3. Cry proteins bind to specific **receptors** on midgut epithelial cells (cadherin-like proteins)

4. Forms **pores** in cell membrane, disrupting ion balance

5. Cell lysis and caterpillar death within 2-3 days

6. Bacterial infection secondary to toxin damage

**Advantages**:

**Specificity**: Only affects target insect larvae; other insects unharmed

**Safety**: Non-toxic to mammals, birds, fish, plants

**Selectivity**: Integrated Pest Management (IPM) compatible; allows retention of beneficial insects

**Persistence**: Spores remain active on plant surface for several days

**Genetic Engineering Application**: **Bt-toxin genes** integrated into crop plant genomes

Producing **Bt-transgenic crops** (Bt-cotton, Bt-maize, Bt-brinjal)

Plants constitutively express Cry proteins in plant tissues

Caterpillars feeding on transgenic plants ingest toxin and die

Reduces pesticide spraying requirement

Bt-cotton successfully cultivated in several Indian states (Maharashtra, Gujarat, Karnataka)

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Fungal Biocontrol: Trichoderma

**Organism**: *Trichoderma* species (free-living fungi)

**Habitat**: Naturally abundant in **root ecosystems** (rhizosphere)

**Mechanism of Action**:

**Hyperparasitism**: Directly parasitizes pathogenic fungal pathogens

**Competition**: Competes with pathogens for nutrients, water, and space

**Antibiotic production**: Secretes antifungal metabolites

**Enzyme production**: Produces cellulases and proteases that degrade pathogen cell walls

**Pathogens Controlled**:

*Fusarium* species (causes wilting, seedling diseases)

*Rhizoctonia* species (causes damping-off in seedlings)

*Sclerotium* species (soil-borne pathogen)

*Pythium* species (causes root rot)

**Advantages**:

Non-pathogenic to plants

Enhances plant growth through nutrient mobilization

Environmentally safe

Can be applied as seed treatment or soil amendment

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Viral Biocontrol: Baculoviruses

**Organism**: Genus **Nucleopolyhedrovirus** (NPV) and other baculoviruses

**Host Specificity**:

Pathogens of insects and other arthropods

**Narrow spectrum**: Each baculovirus species typically infects single insect species or closely related species

Do not infect plants, mammals, birds, fish, or non-target insects

**Viral Structure and Replication**:

Enveloped double-stranded DNA viruses

Occlusion bodies: Viral particles embedded in crystalline protein matrix (polyhedrin)

Insects ingest occlusion bodies while feeding on plants

Viral replication in midgut epithelial cells → insect death in 7-14 days

**Mechanism of Action**:

1. Larvae consume plant leaves with viral occlusion bodies

2. Viral particles released in midgut

3. Infection of epithelial cells and fat body (energy storage tissue)

4. Viral replication and cell lysis

5. Larval death; viral particles released back to environment

**Advantages**:

**Species-specific**: Kills target insect pest without affecting other organisms

**Ecological safety**: Zero negative impacts on plants, mammals, birds, fish, or non-target insects

**IPM compatibility**: Allows conservation of beneficial predatory and parasitic insects

**Ecologically sensitive area application**: Safe for use in protected ecosystems and organic farms

**Self-perpetuating**: Virus can recycle through pest population if conditions favorable

**Limitations**:

Slower action than chemical pesticides (7-14 days vs. hours)

Dependent on pest feeding behavior

Affected by environmental conditions (sunlight degrades virus, rainfall removes from leaves)

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MICROBES AS BIOFERTILISERS

**Biofertiliser Definition**: Living microorganisms or their products that **enrich the nutrient quality of soil** by increasing bioavailable forms of essential plant nutrients (nitrogen, phosphorus, potassium)

**Environmental Context**:

Overuse of **chemical fertilizers** contributes significantly to environmental pollution

Water eutrophication from nitrogen and phosphorus runoff

Soil degradation and loss of soil microbiota

Growing movement toward **organic farming** and sustainable agriculture

Biofertilisers provide sustainable, cost-effective alternative

Major Biofertiliser Sources

#### 1. Nitrogen-Fixing Bacteria

**Symbiotic Nitrogen-Fixing Bacteria: Rhizobium**

**Organism**: Gram-negative rod-shaped bacterium *Rhizobium* species

**Symbiosis**:

Forms mutualistic relationship with **legume plants** (family Fabaceae)

Infection process:

1. Rhizobia enter root hair through infection thread (tip-derived tubular structure)

2. Migrate through cortex cells into root nodule cells

3. Undergo morphological differentiation into **bacteroids** (specialized form)

4. Become surrounded by **peribacteroid membrane** (host-derived)

**Nitrogen Fixation**:

Mechanism: Catalyzed by enzyme **nitrogenase** complex (MoFe protein and Fe protein)

Reaction: N₂ + 8H⁺ + 8e⁻ → 2NH₃ (ammonia)

**Anaerobic environment** in nodule maintained by oxygen-binding protein **leghemoglobin** (plant-synthesized, gives reddish color to nodule)

Ammonia assimilated into **amino acids** via glutamine synthetase and GOGAT pathways

**Products**:

Plant receives bioavailable nitrogen compounds (amino acids, amides)

Excess nitrogen compounds diffuse into soil

Bacteroids receive photosynthetically produced sugars from plant (energy source)

**Legume Crops Inoculated with Rhizobium**:

**Pulses**: Chickpea, pigeon pea, mung bean, urad

**Oil seeds**: Soybean, groundnut

**Fodder**: Clover, lucerne

**Vegetables**: French beans, peas

**Application**: Legume seeds coated with Rhizobium culture before planting; bacteria establish nodules within 2-3 weeks

**Benefits**:

Provides 100-300 kg/hectare of fixed nitrogen annually

Reduces chemical nitrogen fertilizer requirement

Improves soil nitrogen status for subsequent crops

Cost-effective: One-time inoculation provides season-long benefit

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**Free-Living Nitrogen-Fixing Bacteria: Azospirillum**

**Organism**: Gram-negative, spiral-shaped bacterium *Azospirillum brasilense* and *A. lipoferum*

**Habitat**: **Rhizosphere** (root vicinity) and root surfaces of non-leguminous plants (cereals, grasses)

**Nitrogen Fixation**:

Free-living (not symbiotic) anaerobic nitrogenase enzyme

Fix nitrogen under microaerophilic conditions (low O₂ tension)

Convert atmospheric N₂ to ammonia

Ammonia released into rhizosphere and absorbed by plant roots

**Additional Benefits**:

**Plant hormone production**: Synthesize auxins, gibberellins, and cytokinins

Enhanced root development and plant growth

Improved water and nutrient uptake

Increased crop yield by 10-30%

**Application**: Seed treatment or soil inoculation; particularly effective in cereal crops (rice, wheat, maize, sorghum)

**Synergistic Combination**: Often used together with Rhizobium in legume crops to maximize nitrogen availability

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#### 2. Phosphate-Solubilizing Microorganisms

**Problem**: Most soil phosphorus exists as **insoluble compounds** (calcium phosphate, iron phosphate, aluminum phosphate) unavailable to plants despite high total phosphorus content

**Mechanism**:

Certain bacteria and fungi produce **organic acids** (citric, malic, gluconic acids)

Organic acids **chelate** cations (Ca²⁺, Fe³⁺, Al³⁺) binding insoluble phosphate

Release **soluble phosphate** (PO₄³⁻) available for plant uptake

Example reaction: Ca₃(PO₄)₂ + organic acid → soluble phosphate + chelate complex

**Key Microorganisms**:

**Bacteria**: *Bacillus megaterium*, *Bacillus polymyxa*, *Pseudomonas fluorescens*

**Fungi**: *Aspergillus niger*, *Penicillium species*

**Application**: Applied to soil or seeds; colonize rhizosphere and solubilize native soil phosphorus

**Benefits**:

Increases bioavailable phosphorus

Reduces phosphate fertilizer requirement

Cost-effective phosphate management

Prevents excessive phosphate application (source of water pollution)

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#### 3. Mycorrhizal Associations

**Mycorrhiza Definition**: Mutualistic association between **fungal hyphae** and plant **root cells**

**Mechanism of Nutrient Enhancement**:

Fungal hyphae extend beyond root depletion zone, exploring larger soil volume

Hyphae absorb **water, phosphorus, potassium, zinc, iron** from soil

Nutrients transported through hyphae to root cells

Plant provides **photosynthetic sugars** to fungus (carbohydrates)

Nutrient exchange across symbiotic interface

**Benefits to Plant**:

**Phosphorus uptake**: Particularly enhanced; fungal partners highly efficient at phosphate solubilization

**Water uptake**: Improved drought tolerance through enhanced water absorption

**Trace mineral uptake**: Increased zinc, iron, copper, manganese availability

**Disease resistance**: Physical barrier against pathogens; antifungal compounds produced

**Enhanced growth**: Larger root system exploration leads to better nutrition

**Common Mycorrhizal Fungi**:

**Glomus species**, **Acaulospora**, **Gigaspora** (arbuscular mycorrhizal fungi)

*Amanita*, *Boletus*, *Pinus* associations (ectomycorrhizal in forest trees)

**Agricultural Application**:

Applied as soil inoculant containing fungal spores and fragments

Forms effective associations in less than one growing season

Particularly effective in phosphorus-deficient soils

Used in vegetable nurseries, fruit orchards, and field crops

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#### 4. Cyanobacteria as Nitrogen Source

**Cyanobacteria** (formerly blue-green algae): Photosynthetic prokaryotes with **nitrogen-fixing capability**

**Key Species**: *Nostoc*, *Anabaena*, *Oscillatoria*, *Tolypothrix*

**Nitrogen Fixation Mechanism**:

Contain **heterocysts**: Specialized cells with thick cell walls and reduced photosynthetic apparatus

Heterocysts provide anaerobic microenvironment for nitrogenase enzyme

N₂ fixation: N₂ + 8H⁺ + 8e⁻ → 2NH₃

Oxygen evolution in photosynthetic vegetative cells; oxygen scavenged by heterocysts

**Habitat**:

Aquatic and wetland ecosystems

Associate with **rice paddies** (major agricultural region)

Fix nitrogen in flooded soil conditions where Azospirillum activity is reduced

**Application in Rice Cultivation**:

Algal cultures applied to flooded rice paddies

Free-living nitrogen fixation in anaerobic conditions

Contributes 20-30 kg/hectare fixed nitrogen annually

Particularly important in low-input traditional rice farming systems

**Additional Benefits**:

Produce bioactive compounds (vitamins, growth promoters)

Increase soil organic matter

Improve soil structure and water retention

Release phosphate through organic acid production

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Advantages of Biofertilisers Over Chemical Fertilizers

| Aspect | Biofertilisers | Chemical Fertilizers |

|---|---|---|

| **Environmental Impact** | Non-polluting, biodegradable | Pollution of water, soil; eutrophication |

| **Sustainability** | Renewable, continuous production | Non-renewable (mining-dependent) |

| **Cost** | Low initial cost; self-perpetuating | High recurring cost |

| **Soil Health** | Improves soil structure, microbiota diversity | Degrades soil structure; kills beneficial microbes |

| **Nutrient Bioavailability** | Increases available nutrient forms | Provides readily available but potentially excessive nutrients |

| **Application Timing** | Applied before planting; long-term effect | Requires multiple applications during season |

| **Pollution** | Zero pollution risk | Groundwater contamination; eutrophication |

| **Synergistic Benefits** | Plant growth hormone production, disease resistance | None; single nutrient source |

Integrated Nutrient Management (INM)

**Modern agricultural approach** combining biofertilisers with reduced chemical fertilizer doses:

Application of **Rhizobium** + **Phosphate-solubilizing bacteria** + **mycorrhizae** in legume crops

Application of **Azospirillum** + **cyanobacteria** in cereal crops

**50% reduction** in chemical nitrogen and phosphorus fertilizer while maintaining yields

Cost savings: 30-40% reduction in fertilizer expenses

Environmental protection through reduced chemical inputs

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SUMMARY TABLE: MICROBES IN HUMAN WELFARE

| Application | Microorganism | Product/Function | Substrate |

|---|---|---|---|

| **Curd Production** | *Lactobacillus* (LAB) | Coagulation, vitamin B₁₂, probiotic | Milk |

| **Bread Making** | *Saccharomyces cerevisiae* | CO₂ production (leavening) | Dough |

| **Cheese (Swiss)** | *Propionibacterium sharmanii* | CO₂ (holes), flavor | Milk |

| **Beverages** | *Saccharomyces cerevisiae* | Ethanol fermentation | Fruit juice, grains |

| **Penicillin** | *Penicillium notatum* | Antibiotic; cell wall inhibition | Culture medium |

| **Citric Acid** | *Aspergillus niger* | Industrial acid | Sugar solution |

| **Streptokinase** | *Streptococcus* (modified) | Clot buster; thrombolytic | Culture medium |

| **Sewage Treatment** | Various aerobic heterotrophs | BOD reduction through mineralization | Sewage |

| **Biogas Production** | *Methanobacterium* | Methane from cellulose | Cattle dung |

| **Bt Biocontrol** | *Bacillus thuringiensis* | Cry protein; caterpillar death | Transgenic plants |

| **Fungal Biocontrol** | *Trichoderma* | Pathogen hyperparasitism | Root ecosystem |

| **Nitrogen Fixation** | *Rhizobium* | N₂ to NH₃ conversion | Legume nodules |

| **Nitrogen Fixation