🦠 Microbes in Human Welfare 🌟

Introduction to Microbes

Microbes, or microorganisms, are tiny living organisms that are typically invisible to the naked eye, requiring a microscope for observation. Despite their microscopic size, they are ubiquitous, found in virtually every habitat on Earth, including soil, water, air, and even within the bodies of plants, animals, and humans. They can thrive in extreme conditions such as deep inside geysers (up to 100°C), under thick layers of snow, and in highly acidic environments.

Microbes are incredibly diverse, encompassing protozoa, bacteria, fungi, viruses, viroids, and prions. While some microbes are pathogenic and cause diseases, a vast number of them are incredibly beneficial and play crucial roles in human welfare across various sectors, from household products to industrial processes, environmental management, and agriculture.

🏡 Microbes in Household Products

Microbes play an indispensable role in the production of many common household food items, transforming raw ingredients through fermentation processes.

1. Curd Production:
   • Microorganisms like Lactobacillus and others commonly called Lactic Acid Bacteria (LAB) are used.
   • LAB grow in milk, producing acids that coagulate and partially digest milk proteins, converting milk into curd.
   • A small amount of curd (inoculum/starter) contains millions of LAB, which multiply at suitable temperatures.
   • Benefit: Improves nutritional quality by increasing Vitamin B₁₂. LAB also play a beneficial role in our stomach by checking disease-causing microbes.
2. Dough Fermentation:
   • Dough for foods like dosa and idli is fermented by bacteria, producing CO₂ gas, which gives the puffed-up appearance.
   • Bread dough is fermented using baker's yeast (Saccharomyces cerevisiae), also producing CO₂.
3. Traditional Drinks and Foods:
   • Toddy: A traditional drink in southern India, made by fermenting sap from palms.
   • Microbes are also used to ferment fish, soybean, and bamboo shoots to create various food products.
4. Cheese Making:
   • One of the oldest food items where microbes are used.
   • Different varieties of cheese have characteristic texture, flavor, and taste, determined by the specific microbes used.
   • Swiss Cheese: Large holes are due to the production of a large amount of CO₂ by the bacterium Propionibacterium sharmanii.
   • Roquefort Cheese: Ripened by growing specific fungi (e.g., Penicillium roqueforti) on them, which imparts a particular flavor.

🏭 Microbes in Industrial Products

Microbes are extensively used in industries for the large-scale synthesis of valuable products, including beverages, antibiotics, organic acids, enzymes, and other bioactive molecules. Industrial production typically occurs in large vessels called fermentors or bioreactors.

1. Fermented Beverages (Alcoholic Drinks)

Yeasts, particularly Saccharomyces cerevisiae (also known as brewer's yeast), have been used for centuries to produce alcoholic beverages through fermentation of malted cereals and fruit juices to produce ethanol. The type of raw material and processing (with or without distillation) determine the final product.

1. Fermentation Reaction:

   Glucose (from raw material) &xrightarrow{\text{Yeast (anaerobic)}} $ Ethanol + Carbon Dioxide + Energy

2. Types of Alcoholic Drinks:
   1. Without Distillation: These beverages have lower alcohol content.
      • Wine: Produced from fermented fruit juices (e.g., grapes). Alcohol content typically 9-14%.
      • Beer: Produced from fermented malted cereals (e.g., barley). Alcohol content typically 4-6%.
   2. With Distillation: These beverages have higher alcohol content as ethanol is concentrated through distillation of the fermented broth.
      • Whisky: From fermented cereals (e.g., barley, rye, corn). Alcohol content typically 40-50%.
      • Brandy: From distilled wine (fruit juice). Alcohol content typically 40-60%.
      • Rum: From fermented molasses (sugarcane byproduct). Alcohol content typically 40-60%.
      • Gin: From fermented rye or barley, often flavored with botanicals. Alcohol content typically 35-50%.
      • Vodka: From fermented potato or cereals. Alcohol content typically 35-50%.
      • Sake: From fermented rice. Alcohol content typically 15-20%.
3. Other Yeasts in Beverage Production:
   • Saccharomyces ellipsoideus (Wine Yeast)
   • S. sake (Sake Yeast)
   • S. pireformis (Ginger/Ale Yeast)

2. Antibiotics

Antibiotics (Greek: 'anti' - against, 'bios' - life) are chemical substances produced by certain microbes that can kill or retard the growth of other (disease-causing) microbes. They are considered one of the most significant discoveries of the 20th century, revolutionizing the treatment of infectious diseases.

1. Discovery of Penicillin:
   • Accidental Discovery: Alexander Fleming, while working on Staphylococci bacteria, observed a mold (fungus) growing in an unwashed culture plate that prevented the growth of Staphylococci.
   • He identified the mold as Penicillium notatum and named the chemical produced by it Penicillin.
   • Full Potential: Its full potential as an effective antibiotic was later established by Ernest Chain and Howard Florey.
   • Nobel Prize: Fleming, Chain, and Florey were jointly awarded the Nobel Prize in 1945 for this discovery.
2. Common Antibiotics and Their Sources:

   Antibiotic	Source Microbe	Type of Microbe
   Penicillin	Penicillium notatum	Fungus
   Streptomycin	Streptomyces griseus	Bacterium (Actinomycete)
   Bacitracin	Bacillus subtilis	Bacterium
   Terramycin	Streptomyces rimosus	Bacterium (Actinomycete)
   Tetracycline	Streptomyces aureofaciens	Bacterium (Actinomycete)
   Cephalosporin	Cephalosporium acremonium	Fungus
   Chloramphenicol	Streptomyces venezuelae	Bacterium (Actinomycete)
   Erythromycin	Streptomyces erytheus	Bacterium (Actinomycete)

3. Impact: Antibiotics have greatly improved our capacity to treat deadly diseases such as plague, whooping cough (kali khansi), diphtheria (gal ghotu), leprosy (kusht rog), and pneumonia, which previously killed millions.

3. Chemicals (Organic Acids, Alcohols) and Enzymes

Microbes are vital for the commercial and industrial production of various organic acids, alcohols, and enzymes.

1. Organic Acid Producers:
   • Citric Acid: Aspergillus niger (a fungus).
   • Acetic Acid: Acetobacter aceti (a bacterium).
   • Butyric Acid: Clostridium butylicum (a bacterium).
   • Lactic Acid: Lactobacillus (a bacterium).
   • Fumaric Acid: Rhizopus nigricans (a fungus).
   • Gluconic Acid: Aspergillus, Penicillium, Mucor (fungi).
   • Oxalic Acid: Aspergillus niger (a fungus).
2. Enzyme Producers and Uses:
   • Lipases: Produced by microbes like Candida lipolytica. Used in detergent formulations to remove oily stains from laundry.
   • Pectinases and Proteases: Produced by microbes like Aspergillus niger. Used to clarify bottled fruit juices, making them clearer than homemade juices.
   • Streptokinase: Produced by the bacterium Streptococcus and modified by genetic engineering. Used as a 'clot buster' for removing blood clots from the vessels of patients who have suffered myocardial infarction (heart attack).
   • Rennet: Produced by microbes like Mucor. Used for manufacturing cheese.
   • Alpha Amylase: Produced by microbes like Rhizopus japonicus. Used for digestion of starch and softening of bread.

4. Other Bioactive Molecules

Beyond traditional industrial products, microbes also produce complex bioactive molecules with significant pharmaceutical applications.

1. Cyclosporin A:
   • Produced by the fungus Trichoderma polysporum.
   • Used as an immunosuppressive agent in organ-transplant patients to prevent rejection of the transplanted organ.
2. Statins:
   • Produced by the yeast Monascus purpureus.
   • Commercialized as blood-cholesterol lowering agents.
   • Mechanism: They act by competitively inhibiting the enzyme responsible for cholesterol synthesis in the body.

💧 Microbes in Sewage Treatment

Large quantities of wastewater, primarily human excreta and organic matter, are generated daily in cities and towns, forming what is known as sewage. Direct discharge of untreated sewage into natural water bodies like rivers and streams causes severe pollution and spreads water-borne diseases. Therefore, sewage is treated in Sewage Treatment Plants (STPs) to reduce its polluting potential before disposal.

The treatment of wastewater is primarily carried out by heterotrophic microbes naturally present in the sewage and involves two main stages:

1. Primary Treatment (Physical Treatment)

This stage involves the physical removal of large and small particles from the sewage through filtration and sedimentation.

1. Sequential Filtration: Initially, floating debris (e.g., plastic, rags) is removed by passing the sewage through wired mesh screens of progressively smaller pore sizes.
2. Sedimentation (Grit Chamber): After filtration, the sewage is passed into grit chambers where the grit (soil and small pebbles) settles down due to gravity.
3. Primary Settling Tank: The sewage then enters a primary settling tank, where most of the suspended solids settle to form the primary sludge. The supernatant liquid, called the effluent, is then directed for secondary treatment.

2. Secondary Treatment (Biological Treatment)

This stage involves significant microbial activity to reduce the organic matter in the effluent from primary treatment.

1. Aeration Tanks: The primary effluent is pumped into large aeration tanks. Here, it is constantly agitated mechanically, and air is pumped into it.
2. Floc Formation: This aeration and agitation promote the vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments, forming mesh-like structures).
3. BOD Reduction: As these microbes grow, they consume the major part of the organic matter in the effluent. This significantly reduces the Biochemical Oxygen Demand (BOD) of the effluent.
   • BOD Definition: BOD refers to the amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. It is an indirect measure of the organic matter present in the water.
   • Significance: A higher BOD indicates a greater polluting potential of the wastewater. Sewage is treated until its BOD is significantly reduced.
4. Settling Tank (Activated Sludge): Once the BOD is reduced, the effluent is passed into a settling tank where the bacterial flocs are allowed to sediment. This sediment is called activated sludge.
5. Inoculum Return: A small portion of the activated sludge is pumped back into the aeration tank to serve as an inoculum (starter) for the next batch of incoming effluent.
6. Anaerobic Sludge Digesters: The remaining major part of the activated sludge is pumped into large tanks called anaerobic sludge digesters. Here, other types of bacteria, which grow anaerobically, digest the bacteria and fungi in the sludge.
7. Biogas Production: During this anaerobic digestion, bacteria produce a mixture of gases such as methane (CH₄), hydrogen sulphide (H₂S), and carbon dioxide (CO₂). These gases form biogas, which is inflammable and can be used as a source of energy.
8. Final Discharge: The effluent from the secondary treatment plant is generally clean enough to be released into natural water bodies like rivers and streams.

Microbes play a major role in treating millions of gallons of wastewater daily, a methodology practiced for over a century. No man-made technology has yet been able to rival microbial sewage treatment.

Government Initiatives: The Ministry of Environment and Forests has initiated plans like the Ganga Action Plan (GAP) and Yamuna Action Plan (YAP) to reduce river pollution by building more STPs.

💨 Microbes in Production of Biogas

Biogas is a combustible mixture of gases, primarily methane, produced by the microbial activity on organic matter. Microbes produce different types of gaseous end-products during their growth and metabolism, depending on the microbes involved and the organic substrates they utilize.

1. Methanogens: Certain bacteria, collectively called methanogens (e.g., Methanobacterium), grow anaerobically on cellulosic material and produce large amounts of methane along with CO₂ and H₂.
   • Habitat: Commonly found in anaerobic sludge during sewage treatment. They are also present in the rumen (a part of the stomach) of cattle, where they help in the breakdown of cellulose, playing an important role in cattle nutrition.
2. Gobar Gas (Biogas from Cattle Dung):
   • Cattle excreta (dung) is rich in methanogens and cellulosic material. This makes dung an excellent substrate for biogas generation.
   • Biogas Plant Structure: Consists of a concrete tank (10-15 feet deep) where bio-wastes and a slurry of dung are fed. A floating cover is placed over the slurry, which rises as gas is produced.
   • Gas Collection and Use: An outlet pipe supplies biogas to nearby houses for cooking and lighting.
   • Spent Slurry: The digested slurry is removed through another outlet and can be used as a rich fertilizer.
3. Biogas Composition:
   • Methane (CH₄): 60-70% (predominant)
   • Carbon dioxide (CO₂): 25-35%
   • Hydrogen sulphide (H₂S): 1-5%
   • Hydrogen (H₂)
4. Development in India: The technology of biogas production was developed in India mainly due to the efforts of the Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

🐛 Microbes as Biocontrol Agents

Biocontrol refers to the use of biological methods for controlling plant diseases and pests, as an alternative to harmful chemical insecticides and pesticides. Modern organic farming emphasizes biodiversity to maintain ecological balance, where pests are kept at manageable levels by natural predators and parasites, rather than being eradicated indiscriminately.

1. Advantages of Biocontrol:
   • Reduces dependence on toxic chemicals and pesticides, which pollute the environment (soil, groundwater, fruits, vegetables, crop plants).
   • Promotes biodiversity and a sustainable ecosystem.
   • Avoids killing useful life forms along with harmful ones.
2. Examples of Biocontrol Agents:
   1. Insects as Predators:
      • Ladybird beetle (with red and black markings): Useful to get rid of aphids.
      • Dragonflies: Useful to control mosquitoes.
   2. Microbial Biocontrol Agents:
      • Bacillus thuringiensis (Bt): A bacterium available as dried spores. When sprayed on plants (e.g., brassicas, fruit trees) and eaten by insect larvae (e.g., butterfly caterpillars), it releases a toxin in the larval gut, killing them. It is species-specific and harmless to other insects.
        • Bt-cotton: Through genetic engineering, Bt toxin genes have been introduced into plants, making them resistant to insect pests.
      • Fungus Trichoderma: Free-living fungi common in root ecosystems. They are effective biocontrol agents against several plant pathogens.
      • Baculoviruses: Pathogens that attack insects and other arthropods. The majority used as biological control agents belong to the genus Nucleopolyhedrovirus.
        • Characteristics: Species-specific, narrow-spectrum insecticidal applications. They have no negative impacts on plants, mammals, birds, fish, or non-target insects, making them ideal for Integrated Pest Management (IPM) programs and ecologically sensitive areas.

🌱 Microbes as Biofertilisers

Biofertilisers are microorganisms that enrich the nutrient quality of the soil, serving as a sustainable alternative to chemical fertilizers, which contribute significantly to environmental pollution. They enhance soil fertility by adding specific nutrients.

The main sources of biofertilisers are bacteria, fungi, and cyanobacteria.

1. Bacteria as Biofertilisers:
   1. Symbiotic Nitrogen-Fixing Bacteria:
      • Rhizobium: Forms symbiotic associations with the root nodules of leguminous plants (e.g., peas, beans, clover, alfalfa, soybean). It fixes atmospheric nitrogen into organic forms that plants can utilize, significantly increasing soil fertility.
      • Examples: Rhizobium japonicum (with soybean), R. trifolii (clover group), R. meliloti (alfalfa), R. phaseoli (bean group).
   2. Loose Association Nitrogen-Fixing Bacteria:
      • Certain bacteria live around the roots of higher plants but do not form a strict symbiotic relationship. They obtain exudates from the plant as food and fix nitrogen.
      • Example: Azospirillum.
   3. Free-Living Nitrogen-Fixing Bacteria:
      • These bacteria live freely in the soil and fix atmospheric nitrogen.
      • Examples: Azotobacter, Bacillus polymyxa, Beijerinckia.
2. Cyanobacteria (Blue-Green Algae) as Biofertilisers:
   1. Symbiotic Nitrogen-Fixing Cyanobacteria:
      • Azolla-Anabaena association: Anabaena lives symbiotically in the leaves of the fern Azolla pinnata. This association is used to increase rice yield in paddy fields.
      • Anabaena in Cycas: Anabaena lives in the coralloid roots of Cycas.
   2. Free-Living Nitrogen-Fixing Cyanobacteria:
      • Live freely in the soil and fix nitrogen, adding organic matter and nitrogen to the soil, thus increasing its fertility.
      • Examples: Anabaena, Nostoc, Oscillatoria, Aulosira fertilissima (a nitrogen fixer in rice fields).
3. Fungi (Mycorrhizae) as Biofertilisers:
   • Fungi form symbiotic associations called mycorrhizae with the roots of higher plants (e.g., members of the genus Glomus).
   • Mechanism: The fungal symbiont absorbs phosphorus and other minerals from the soil (which plants might not easily access) and passes them to the plant.
   • Benefits to Plants:
     • Increased absorption of water and minerals (especially phosphorus).
     • Resistance to root-borne pathogens.
     • Tolerance to salinity and drought.
     • Overall increase in plant growth and development.
   • Types of Mycorrhizae:
     • Ectomycorrhizae: Fungus forms a mantle on the root surface, with hyphae penetrating the cortex intercellularly and extending into the soil. (e.g., oaks, pines, Eucalyptus).
     • Endomycorrhizae (Vesicular Arbuscular Mycorrhiza - VAM): Fungal hyphae penetrate the cortex cells of the roots, forming vesicles (storage structures) and arbuscules (finely branched masses for nutrient exchange) intracellularly. (e.g., orchids, woody plants).

Biofertilisers are increasingly used by farmers to replenish soil nutrients and reduce dependence on chemical fertilizers, promoting organic farming practices.

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