Chapter 10: Microbes in Human Welfare

Introduction

Overview of Microorganisms

• Microorganisms (microbes) are organisms invisible to the naked eye, viewed under microscopes.
• They exist everywhere: soil, water, air, inside animals and plants, extreme environments like thermal vents, deep soil, snow layers, acidic sites.
• Microbes include bacteria, fungi, protozoa, microscopic plants, viruses, viroids, and prions.
• Bacteria are living microbes with various shapes and movement structures; viruses are simpler infectious agents.
• Microbes like bacteria and fungi can be cultured on nutrient media to form visible colonies for study.

Memory Aids

• Microbes = tiny life forms everywhere, including extreme habitats.
• Bacteria = living, various shapes; Viruses = non-living, infect cells.
• Culture media help grow microbes visibly as colonies.

Quick Checkpoints

• What environments do microbes inhabit?
• Which microbes are living and which are infectious agents?
• How are microbial colonies formed and studied?

Microbes in Household Products

Microbial Uses in Food

• Dairy products (curd, yogurt, butter, cheese) are made by lactic acid bacteria (LAB) like Lactobacillus.
• LAB ferment milk proteins by producing acids, partially digesting them.
• Curd is made by adding a starter (inoculum) containing LAB to milk at suitable temperatures.
• LAB increase vitamin B12 and inhibit harmful microbes in the gut.
• Streptococcus thermophilus and Lactobacillus bulgaricus make yogurt by curdling milk at ~45°C for 4-6 hours.
• Buttermilk is made using Lactobacillus bulgaricus producing lactic acid and flavor compounds; butter is churned from soured cream.
• Streptococcus cremoris produces lactic acid rapidly; Leuconostoc citrovorum produces flavor compounds like diacetyl giving butter its aroma.
• Cheese is curd separated from whey; types depend on water content: soft (50-80%), semihard (45%), hard (<40%).
• Raw cheese is made by LAB curdling milk; ripened cheese matures with bacteria/fungi for 1-16 months.
• Swiss cheese holes are from CO2 by Propionibacterium shermanii; Penicillium roqueforti ripens Roquefort cheese; Penicillium camemberti ripens Camembert cheese.
• Dough for dosa, idli, and bread is fermented by bacteria and baker's yeast (Saccharomyces cerevisiae), producing CO2 for puffiness.
• Traditional fermented drinks like toddy are made by microbial fermentation of palm sap.
• Microbes ferment fish, soybean, bamboo shoots to make various foods.
• Single cell protein (SCP) like Spirulina, yeast, Fusarium graminearum is microbial biomass used as food/feed, reducing pollution.
• Probiotics are live microbes taken orally to improve health by competing with pathogens and stimulating immunity; examples include Lactobacilli and Streptococci.

Memory Aids

• LAB = key for dairy fermentation and health benefits.
• Curd starter = inoculum with millions of LAB.
• Cheese types depend on water and microbial ripening.
• Baker's yeast = Saccharomyces cerevisiae for bread fermentation.
• Probiotics = friendly bacteria improving gut health.

Quick Checkpoints

• Which microbes produce curd and yogurt?
• How is butter flavor developed microbially?
• What determines cheese types and ripening?
• Which microbe ferments bread dough?
• What are probiotics and their benefits?

Microbes in Industrial Products

Fermented Beverages

• Yeast and some bacteria ferment carbohydrates into ethanol and carbon dioxide using enzyme Zymase.
• Equation: Glucose (C6H12O6) → Ethanol (C2H5OH) + CO2.
• Yeast species: Saccharomyces cerevisiae (brewer's yeast), S. ellipsoideus (wine yeast), S. sake (sake yeast), S. pyriformis (ginger beer yeast).
• Fermentation media vary: barley malt (beer), juniper berries malt (gin), rice (sake), cashew-apple (fenny), potato (vodka), corn/rye (whisky), molasses (rum), fruit juices (wine, brandy).
• Baker's yeast: selected S. cerevisiae strains for baking (flavour, texture).
• Brewer's yeast: used for alcoholic drinks.
• Alcoholic beverages: beer and wine (undistilled), whisky, rum, gin, brandy, vodka, fenny (distilled, hard liquors).
• Fermentation methods:
  • Batch culture: closed system, no nutrient addition after start.
  • Continuous culture: nutrients added continuously, overflow harvested.
  • Fed batch culture: nutrients added gradually to extend growth.

Memory Aids

• "Batch" = closed, no change after start.
• "Continuous" = constant nutrient flow and harvest.
• "Fed batch" = gradual nutrient feeding.
• Yeast species names start with Saccharomyces.

Quick Checkpoints

• What enzyme catalyzes fermentation?
• Difference between baker's and brewer's yeast?
• Examples of distilled vs undistilled beverages?
• Describe batch, continuous, and fed batch cultures.

Antibiotics

Definition and Discovery

• Antibiotics: chemicals from microbes that kill or inhibit other microbes.
• Term origin: "Anti" = against, "bio" = life (against harmful microbes, pro-life for humans).
• Penicillin: first antibiotic discovered by Alexander Fleming from Penicillium notatum.
• Commercial extraction by Ernst Chain and Howard Florey; Nobel Prize 1945.
• Used extensively in WWII for wounded soldiers.
• Other antibiotics followed for various infectious diseases.
• Effective against diseases like plague, whooping cough, leprosy, diphtheria.

Production Process

• Microorganism grown in nutrient medium with controlled pH, temperature, air, anti-foaming agent, and precursors.
• After antibiotic production, microbes removed.
• Antibiotic extracted by precipitation, absorption, or solvent treatment.
• Purified, concentrated, tested, and packed for use.

Characteristics of a Good Antibiotic

• Harmless to host, no side effects.
• Quick action.
• Destroys pathogens effectively.
• Harmless to normal gut microflora.
• Effective against all pathogen strains.

Memory Aids

• Penicillin from Penicillium mould.
• Antibiotics = "Anti-life" for microbes, "Pro-life" for humans.
• Good antibiotic = safe + fast + broad spectrum.

Quick Checkpoints

• Who discovered penicillin?
• What makes an antibiotic good?
• Steps in antibiotic production?
• Diseases treated by antibiotics?

Chemicals, Enzymes and Other Bioactive Molecules

Organic Acids

• Citric acid: produced by Aspergillus niger on carbohydrates; also by yeast Candida lipolytica under iron/manganese deficiency; used in medicines, food preservation, flavouring.
• Acetic acid: produced by Acetobacter aceti from fermented alcohol; used in vinegar, pharmaceuticals, insecticides, plastics.
• Lactic acid: produced by Lactobacillus bulgaricus and L. delbrueckii from starch, molasses, whey; first organic acid produced by microbial fermentation.
• Butyric acid: produced by Clostridium acetobutylicum during fermentation; found in rancid butter.

Enzymes

• Lipases from Candida lipolytica and Geotrichum candidum: remove oily stains in detergents.
• Pectinases from Byssochlamys fulva: used with proteases to clarify bottled juices.
• Streptokinase from Streptococcus: genetically modified clot buster enzyme, also called Tissue Plasminogen Activator (TPA).

Bioactive Molecules

• Cyclosporin-A: produced by Trichoderma polysporum, an 11-membered cyclic oligopeptide; used as immunosuppressant in organ transplantation.
• Statin: produced by yeast Monascus purpureus; lowers blood cholesterol by inhibiting cholesterol synthesis enzyme.

Memory Aids

• Citric acid from Aspergillus, acetic acid from Acetobacter.
• Lactic acid first fermented acid (Scheele, 1789).
• Streptokinase = clot buster = TPA.
• Cyclosporin-A = immunosuppressant.
• Statin = cholesterol lowering.

Quick Checkpoints

• Microbes producing citric and lactic acid?
• Uses of lipases and pectinases?
• Role of streptokinase?
• Function of cyclosporin-A and statin?

Microbes in Sewage Treatment

Process Overview

• Sewage contains human waste, organic matter, and pathogens.
• Must be treated before release to prevent water pollution and diseases.
• Treatment involves primary, secondary, and sometimes tertiary steps.

Primary Treatment

• Removes floating and suspended solids by filtration and sedimentation.
• Sewage passes through grit chamber; heavy particles settle as grit.
• Sedimentation tank concentrates suspended solids as primary sludge; clear liquid is effluent.
• Primary sludge is composted; effluent moves to secondary treatment.

Secondary Treatment

• Biological process using microbes to degrade organic matter.
• Activated sludge system: aeration tanks mix air and sewage to support aerobic microbes.
• Microbes form flocs—bacterial masses held by slime and fungal filaments.
• Microbes digest organic matter, reducing Biochemical Oxygen Demand (BOD) to 10-15% of raw sewage.
• Effluent goes to sedimentation tank; flocs settle as activated sludge.
• Part of activated sludge reused in aeration; rest sent to anaerobic sludge digester.
• Anaerobic microbes digest organic matter and aerobic microbes, producing biogas (CH4, CO2, H2S).

Tertiary Treatment

• Removes nitrates and phosphates by precipitation.
• Expensive step producing water pure enough for drinking.

Memory Aids

• Primary = Physical removal (filtration + sedimentation).
• Secondary = Biological digestion by activated sludge microbes.
• Tertiary = Chemical removal of nutrients (nitrates, phosphates).
• Activated sludge forms flocs for easy settling.
• Biogas from anaerobic digestion = energy source.

Quick Checkpoints

• What solids are removed in primary treatment?
• How do aerobic microbes reduce BOD?
• What is the role of activated sludge?
• Which gases form biogas in anaerobic digestion?
• What pollutants are removed in tertiary treatment?

Sewage Treatment Plant Process

• Sewage enters from homes; debris removed by coarse screen.
• Sand and grit settle by sedimentation.
• Primary clarification settles solids as sludge; clear water moves on.
• Sludge sent to digester for breakdown.
• Aeration adds air to support bacteria in secondary treatment.
• Secondary clarification separates more sludge.
• Disinfection kills harmful microbes using chlorine or UV light.
• Nutrient removal prevents pollution by removing nitrogen and phosphorus.
• Cleaned effluent released safely into water bodies.
• Protects environment and human health by proper wastewater treatment.

River Action Plan

Background and Initiatives

• Before 1985, most cities discharged untreated sewage into rivers causing pollution and diseases.
• Ministry of Environment and Forests initiated sewage treatment plants under National River Conservation Authority.
• Major projects include Ganga Action Plan, Yamuna Action Plan, Sutlej Action Plan, Gomti Action Plan.

Memory Aids

• River Action Plans started post-1985 to reduce river pollution.
• Focus on major Indian rivers with dedicated treatment projects.

Quick Checkpoints

• Why was sewage treatment rare before 1985?
• What is the purpose of National River Conservation Authority?
• Name major river action plans in India.

Microbes in Production of Biogas

Biogas Composition and Microbial Role

• Biogas is a methane-rich fuel produced by bacterial degradation of biological matter under anaerobic conditions.
• Composition: 50-70% methane (CH94), 30-40% carbon dioxide (CO92), 1-5% hydrogen (H2), traces of oxygen (O2), nitrogen (N2), and hydrogen sulfide (H2S).
• Methanogens are anaerobic bacteria that produce methane by breaking down cellulosic material; examples include Methanobacterium and Methanococcus.
• These bacteria are found in anaerobic sludge during sewage treatment and in the rumen of cattle.
• In the rumen, methanogens help digest cellulose, aiding cattle nutrition.
• Cattle dung (gobar) is rich in methanogens and used as raw material for biogas production (gobar gas).
• Anaerobic bacteria digest slurry (cattle dung + water) at 34-48C, producing mainly methane and carbon dioxide.
• Gas buildup during digestion lifts the floating cover of the biogas plant, releasing biogas.

Biogas Plant and Process

• Organic materials (cellulose, hemicellulose, polysaccharides, fats, proteins) enter the digester.
• Solubilisation: decomposer microbes break complex materials into simpler monomers.
• Acidogenesis: fermentative microbes convert monomers into organic acids.
• Methanogenesis: methanogens convert organic acids into biogas (methane, carbon dioxide, hydrogen, nitrogen, hydrogen sulfide).
• Biogas is collected in the gas-holder for fuel use; remaining sludge is used as fertilizer.
• Biogas plant outlets supply gas for cooking and lighting; spent slurry is used as manure.
• Biogas is eco-friendly and pollution-free energy.
• Technology developed mainly by Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

Memory Aids

• Methanogens = methane producers in anaerobic conditions.
• Gobar gas = biogas from cattle dung (gobar).
• Slurry = mixture of dung + water for digestion.
• Stages: Solubilisation → Acidogenesis → Methanogenesis.

Quick Checkpoints

• What microbes produce methane in biogas plants?
• What is the main composition of biogas?
• Where are methanogens commonly found?
• What is the role of slurry in biogas production?
• Which Indian institutes contributed to biogas technology?

Microbes as Biocontrol Agents

Biocontrol Overview

• Biocontrol uses biological methods to manage pests and plant diseases.
• Chemical pesticides are toxic, harmful to humans, animals, and pollute soil and water.
• Biological control reduces chemical pesticide use, lowering environmental pollution.
• Biopesticides include bioherbicides and bioinsecticides.
• Biocontrol maintains pests at manageable levels, preserving beneficial insects and ecosystem stability.
• Biocontrol is non-toxic, biodegradable, and involves a holistic approach.

Memory Aids

• Bio = Biological, Control = Pest management without chemicals.
• Biopesticides = Bioherbicides + Bioinsecticides.
• Biocontrol = Balance pests, protect ecosystem.

Quick Checkpoints

• What is biocontrol and why is it needed?
• How does biocontrol maintain ecosystem stability?
• What are biopesticides?

Examples of Biological Control

Bioinsecticides and Agents

• Bioinsecticides are living organisms (viruses, bacteria, fungi) controlling insect pests.
• Lady bird beetle (Coccinella) controls aphids.
• Dragonflies (Sympetrum) control mosquitoes; called mosquito hawk.
• Trichoderma fungus controls several plant pathogens.
• Baculoviruses (e.g., Nucleopolyhedrovirus) infect and kill specific insect pests without harming others.
• Entomopox virus slows grasshopper development and feeding.
• Bacillus thuringiensis produces insecticidal protein toxin (thurioside) killing insect larvae by disrupting mid-gut ion transport.
• Spores of B. thuringiensis contain cry protein; used in sachets for spraying on plants.
• Transgenic plants expressing B. thuringiensis toxin gene resist insect pests (cotton, tobacco).
• Fungi-based bioinsecticides like Beauveria bassiana control insect populations; safe for warm-blooded animals and water.

Memory Aids

• Lady bird beetle = Aphid control.
• Dragonfly = Mosquito hawk.
• Bacillus thuringiensis = Bt toxin kills larvae.
• Baculoviruses = Species-specific insect killers.
• Trichoderma = Soil fungus pathogen control.

Quick Checkpoints

• Which organisms act as bioinsecticides?
• How does Bacillus thuringiensis kill insect larvae?
• What is the role of baculoviruses in pest control?

Bioherbicides

Weed Control Using Living Organisms

• Bioherbicides are living organisms controlling weeds.
• First bioherbicide (1981) was a mycoherbicide from Phytophthora palmivora controlling milk weed vines.
• Cochineal insect (Cactoblastis cactorum) controls cactus overgrowth in India and Australia.
• Fungal spore products like Devine and Collego control weeds.
• Transgenic crops (tomato, tobacco) with herbicide resistance genes tolerate herbicides, aiding weed control.

Memory Aids

• Bioherbicides = Biological weed killers.
• Cochineal insect = Cactus control.
• Transgenic plants = Herbicide-resistant crops.

Quick Checkpoints

• What are bioherbicides?
• How does Cactoblastis cactorum control cacti?
• What is the role of transgenic plants in weed control?

Other Biocontrol Agents

Integrated Pest Management (IPM)

• IPM reduces agro-chemical pollution and increases productivity.
• Methods include pest starvation, cultural controls, crop rotation, sanitation, and minimizing synthetic pesticides.
• Biological control is emphasized; chemical pesticide use is minimized.
• Mixed cropping with target weeds attracts pests away from main crops.

Memory Aids

• IPM = Combine methods for pest control.
• Minimize chemicals, maximize biological methods.
• Crop rotation and sanitation prevent pest buildup.

Quick Checkpoints

• What is the goal of IPM?
• List key methods used in IPM.
• How does mixed cropping help in pest management?

Microbes as Biofertilisers

Sources and Roles

• Chemical fertilisers cause pollution; organic farming is preferred.
• Biofertilisers are organisms that enrich soil nutrients, especially nitrogen and phosphorus.
• Main biofertiliser sources: bacteria, fungi, and cyanobacteria.
• Rhizobium forms root nodules in legumes, fixing atmospheric nitrogen into usable forms.
• Free-living nitrogen-fixing bacteria: Azospirillum, Azotobacter.
• Fungi form mycorrhiza with plant roots; common partner: Glomus.
• Mycorrhiza fungi absorb phosphorus and enhance plant growth, drought and salinity tolerance, and pathogen resistance.
• Cyanobacteria (e.g., Anabaena, Nostoc, Oscillatoria) fix nitrogen and add organic matter, improving soil fertility.
• Biofertilisers are commercially available and reduce chemical fertiliser use.

Memory Aids

• Biofertilisers = Bacteria + Fungi + Cyanobacteria.
• Rhizobium = Root nodules + Nitrogen fixation.
• Mycorrhiza = Fungi + Roots + Phosphorus uptake.
• Cyanobacteria = Nitrogen fixers + Photosynthetic microbes.
• Free-living bacteria = Azotobacter, Azospirillum.

Quick Checkpoints

• What are biofertilisers and their main sources?
• How does Rhizobium benefit leguminous plants?
• Role of mycorrhiza in plant nutrition?
• Examples of free-living nitrogen-fixing bacteria?
• Why are cyanobacteria important in paddy fields?

Importance of Biofertilisers

Benefits

• Increase plant yield by 15-35%.
• Effective under semi-arid conditions.
• Improve soil texture and fertility.
• Suppress soil pathogens.
• Non-polluting and eco-friendly.
• Produce vitamins and growth-promoting biochemicals.

Memory Aids

• Biofertilisers boost yield and soil health.
• Eco-friendly alternative to chemical fertilisers.
• Help plants resist stress and pathogens.

Quick Checkpoints

• How do biofertilisers improve plant yield?
• What soil conditions do biofertilisers tolerate?
• How do biofertilisers affect soil pathogens?
• What additional substances do biofertilisers produce?