Biology Notes of Chapter 8 Microbes in Human Welfare

Microbes, despite causing diseases, play crucial beneficial roles in human welfare. They are essential components of biological systems and are found everywhere, including extreme environments. This chapter explores their diverse applications beyond causing illness. Microbes or their products are used daily in household items like curd, dosa/idli dough, bread, and cheese. Industrially, they are vital for producing beverages like wine, beer, whisky, brandy, and rum, and critically, antibiotics like Penicillin. Microbes are also indispensable in treating large quantities of sewage to reduce pollution. They are key to producing biogas, a valuable energy source, and function as biocontrol agents against pests and diseases, reducing reliance on toxic chemicals. Furthermore, microbes serve as biofertilisers, enriching soil nutrients and promoting sustainable agriculture.

1. Microbes in Household Products

• Daily Use: Microbes or their products are used daily in various household items.
• Curd Production:
• Micro-organisms like Lactobacillus and other lactic acid bacteria (LAB) grow in milk.
• LAB convert milk to curd.
• During growth, LAB produce acids that coagulate and partially digest milk proteins .
• A small amount of curd acts as inoculum or starter , containing millions of LAB that multiply at suitable temperatures.
• Curd improves milk's nutritional quality by increasing Vitamin B12 .
• In the stomach, LAB are beneficial in checking disease-causing microbes .
• Dough for Dosa and Idli:
• Dough is fermented by bacteria.
• The puffed-up appearance is due to the production of CO2 gas during fermentation.
• Bread Making:
• Dough is fermented using baker's yeast (Saccharomyces cerevisiae) .
• Traditional Drinks and Foods:
• Many traditional drinks and foods are made by microbial fermentation.
• 'Toddy' (southern India) is made by fermenting sap from palms.
• Microbes ferment fish, soybean, and bamboo-shoots for food.
• Cheese Production:
• One of the oldest food items using microbes.
• Different varieties have characteristic texture, flavor, and taste from specific microbes.
• Large holes in Swiss cheese are due to large CO2 production by Propionibacterium sharmanii .
• Roquefort cheese is ripened by growing a specific fungi on it for particular flavor.

2. Microbes in Industrial Products

• Microbes are used to synthesize valuable products industrially.
• Requires growing microbes in large vessels called fermentors (Example shown in Figure 8.4).

2.1 Fermented Beverages

• Microbes, especially yeasts , used for beverages like wine, beer, whisky, brandy, rum.
• Saccharomyces cerevisiae (brewer's yeast, also used for bread) ferments malted cereals and fruit juices to produce ethanol .
• Different alcoholic drinks obtained based on raw material and processing (with or without distillation).
• Wine and beer: Produced without distillation .
• Whisky, brandy, rum: Produced by distillation of the fermented broth.

2.2 Antibiotics

• Regarded as one of the most significant discoveries of the 20th century for human welfare.
• 'Anti' means 'against', 'bio' means 'life'; antibiotics mean 'against life' in context of disease-causing organisms, but 'pro life' for humans.
• Chemical substances produced by some microbes that can kill or retard growth of other (disease-causing) microbes .
• Penicillin:
• The first antibiotic discovered .
• A chance discovery by Alexander Fleming while working on Staphylococci bacteria.
• Observed a mould ( Penicillium notatum ) prevented Staphylococci growth.
• Named the chemical produced Penicillin .
• Full potential established later by Ernest Chain and Howard Florey .
• Extensively used to treat wounded American soldiers in WWII.
• Fleming, Chain, and Florey received the Nobel Prize in 1945 for this discovery.
• Antibiotics greatly improved treatment of deadly diseases like plague, whooping cough, diphtheria, and leprosy.

2.3 Chemicals, Enzymes and other Bioactive Molecules

• Microbes used for commercial/industrial production of organic acids, alcohols, enzymes, and bioactive molecules.
• Organic Acids:
• Citric acid: Aspergillus niger (fungus).
• Acetic acid: Acetobacter aceti (bacterium).
• Butyric acid: Clostridium butylicum (bacterium).
• Lactic acid: Lactobacillus (bacterium).
• Ethanol: Commercial production using Yeast (Saccharomyces cerevisiae) .
• Enzymes:
• Lipases: Used in detergent formulations to remove oily stains.
• Pectinases and Proteases: Used to clarify bottled fruit juices.
• Streptokinase: Produced by Streptococcus (modified by genetic engineering), used as a 'clot buster' to remove blood clots causing heart attacks.
• Bioactive Molecules:
• Cyclosporin A: Produced by the fungus Trichoderma polysporum . Used as an immunosuppressive agent in organ transplant patients.
• Statins: Produced by the yeast Monascus purpureus . Commercialized as blood-cholesterol lowering agents . Acts by inhibiting the enzyme responsible for cholesterol synthesis.

3. Microbes in Sewage Treatment

• Large quantities of waste water (sewage) are generated daily.
• Sewage contains human excreta, large organic matter amounts, and pathogenic microbes.
• Cannot be discharged directly into natural water bodies due to pollution risk.
• Treated in Sewage Treatment Plants (STPs) to make it less polluting.
• Treatment is done by heterotrophic microbes naturally present in sewage .
• Carried out in two stages:
• Primary Treatment:
• Physical removal of particles (large and small).
• Involves filtration and sedimentation .
• Floating debris removed by sequential filtration.
• Grit (soil, small pebbles) removed by sedimentation.
• Solids that settle form the primary sludge .
• Supernatant forms the effluent .
• Effluent from primary tank goes to secondary treatment.
• Secondary Treatment (Biological Treatment):
• Primary effluent passed into large aeration tanks (Example shown in Figure 8.6).
• Constantly agitated mechanically and air is pumped in.
• Allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments).
• These microbes consume major part of the organic matter in effluent while growing.
• Significantly reduces the BOD (Biochemical Oxygen Demand) of the effluent.
• BOD: Amount of oxygen consumed if all organic matter in 1 liter of water were oxidized by bacteria.
• BOD test measures rate of oxygen uptake by microbes, indirectly measuring organic matter .
• Higher BOD = More polluting potential .
• Sewage is treated until BOD is significantly reduced.
• Effluent passed to a settling tank; bacterial flocs sediment, forming activated sludge .
• A small part of activated sludge is pumped back to aeration tank as inoculum .
• Remaining sludge pumped into anaerobic sludge digesters .
• Anaerobic bacteria digest the bacteria and fungi in the sludge.
• Digestion produces a mixture of gases: methane, hydrogen sulphide, carbon dioxide .
• These gases form biogas , usable as fuel.
• Effluent from secondary treatment is generally released into natural water bodies.
• Microbial treatment of sewage has been practiced for over a century and is highly effective.
• Increasing urbanization leads to more sewage, but insufficient STPs lead to discharge of untreated sewage, causing pollution and water-borne diseases.
• Ganga Action Plan and Yamuna Action Plan aim to build more STPs to treat sewage before discharge.

4. Microbes in Production of Biogas

• Biogas: Mixture of gases (predominantly methane) produced by microbial activity, used as fuel.
• Type of gas depends on microbes and organic substrates.
• Fermentation of dough, cheese, beverages mainly produces CO2 .
• Certain bacteria growing anaerobically on cellulosic material produce large amounts of methane, CO2, and H2 .
• These bacteria are collectively called methanogens .
• A common methanogen is Methanobacterium .
• Methanogens found in anaerobic sludge during sewage treatment.
• Also present in the rumen of cattle , helping break down cellulose.
• Cattle excreta ( dung or gobar ) is rich in these bacteria.
• Dung is used for biogas generation ( gobar gas ).
• Biogas plant:
• Concrete tank (10-15 ft deep) for bio-wastes and dung slurry.
• Floating cover rises as gas is produced.
• Outlet pipe supplies biogas to houses.
• Spent slurry removed via another outlet, usable as fertiliser .
• Biogas plants are common in rural areas where cattle dung is available.
• Biogas used for cooking and lighting.
• Technology developed in India by IARI and KVIC .

5. Microbes as Biocontrol Agents

• Biocontrol: Using biological methods to control plant diseases and pests.
• Modern society relies heavily on toxic chemicals (insecticides, pesticides, weedicides).
• Chemicals are toxic to humans/animals and pollute the environment (soil, groundwater, food).
• Biological control in agriculture relies on natural predation and a holistic approach .
• Organic farming belief: Biodiversity furthers health and sustainability.
• Aim is not eradication of pests, but keeping them at manageable levels using checks and balances within the ecosystem.
• Relies on understanding webs of interaction between organisms.
• Biocontrol reduces dependence on toxic chemicals.
• Requires familiarization with field life forms (predators, pests), their life cycles, feeding patterns, habitats.
• Examples of Biocontrol Agents:
• Ladybird beetle: Useful against aphids.
• Dragonflies: Useful against mosquitoes.
• Bacteria Bacillus thuringiensis (Bt):
• Controls butterfly caterpillars.
• Available as dried spores mixed with water, sprayed on plants.
• Eaten by insect larvae, toxin released in gut, killing larvae.
• Kills caterpillars but leaves other insects unharmed.
• Bt toxin genes introduced into plants via genetic engineering (e.g., Bt-cotton ) make plants pest-resistant.
• Fungus Trichoderma:
• Used for treating plant diseases.
• Free-living fungi common in root ecosystems.
• Effective biocontrol agents of several plant pathogens.
• Baculoviruses:
• Pathogens attacking insects and other arthropods.
• Majority used are in genus Nucleopolyhedrovirus .
• Excellent candidates for species-specific, narrow spectrum insecticidal applications.
• No negative impacts on plants, mammals, birds, fish, or non-target insects.
• Desirable for conserving beneficial insects in Integrated Pest Management (IPM) or treating sensitive areas.

6. Microbes as Biofertilisers

• Environmental pollution from chemical fertilisers is a major concern.
• Push towards organic farming and use of biofertilisers.
• Biofertilisers: Organisms that enrich the nutrient quality of the soil .
• Main sources: bacteria, fungi, and cyanobacteria .
• Bacteria:
• Rhizobium: Symbiotic association with leguminous plant roots (nodules).
• Fix atmospheric nitrogen into organic forms used by plants.
• Azospirillum and Azotobacter: Free-living in soil.
• Fix atmospheric nitrogen, enriching soil nitrogen content.
• Fungi:
• Form symbiotic associations with plants ( mycorrhiza ).
• Many Glomus species form mycorrhiza.
• Fungal symbiont absorbs phosphorus from soil and passes it to the plant.
• Benefits to plants include resistance to root pathogens, tolerance to salinity/drought, increased growth/development.
• Cyanobacteria (Blue Green Algae):
• Autotrophic microbes in aquatic and terrestrial environments.
• Many fix atmospheric nitrogen (e.g., Anabaena, Nostoc, Oscillatoria).
• Important biofertiliser in paddy fields.
• Add organic matter and increase soil fertility.
• Commercial biofertilisers are available, used by farmers to replenish nutrients and reduce chemical fertiliser dependence.

Exam Focus: Differentiations

• Beverages with/without distillation :
• Without Distillation: Wine, Beer
• With Distillation: Whisky, Brandy, Rum
• Primary vs. Secondary Sewage Treatment :
• Primary Treatment: Physical process (filtration, sedimentation). Removes large/small particles, floating debris, grit. Produces primary sludge and effluent.
• Secondary Treatment: Biological process using microbes (aerobic and anaerobic). Reduces organic matter (lowers BOD), forms activated sludge, produces biogas.
• Types of Microbial Biofertilisers :
• Bacteria (e.g., Rhizobium, Azospirillum, Azotobacter): Primarily fix atmospheric nitrogen.
• Fungi (e.g., Glomus in Mycorrhiza): Absorb phosphorus from soil for plants.
• Cyanobacteria (e.g., Anabaena, Nostoc): Fix atmospheric nitrogen and add organic matter.

Frequently Asked Questions (FAQs)

1. What are the useful applications of lactic acid bacteria (LAB) in the household?
   
   LAB convert milk into curd and improve its nutritional quality by increasing Vitamin B12. They also play a beneficial role in the stomach by checking disease-causing microbes. They are also used in fermenting dough for foods like dosa and idli.
   
   
2. How do microbes help in treating sewage waste water?
   
   In secondary treatment, aerobic microbes in flocs consume organic matter in the effluent, significantly reducing BOD. Anaerobic bacteria in sludge digesters then digest the activated sludge, producing biogas.
   
   
3. Name two examples of microbes used as biocontrol agents and their targets.
   
   The bacterium Bacillus thuringiensis (Bt) is used to control butterfly caterpillars. The fungus Trichoderma is used as a biocontrol agent against several plant pathogens.