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Chapter 8 – Microbes in Human Welfare

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Microbes in Household Products

Microbes are used daily in the production of food items.

  • LAB (Lactic Acid Bacteria): Microorganisms like Lactobacillus grow in milk and convert it into curd. LAB produces acids that coagulate and partially digest milk proteins. It improves nutritional quality by increasing Vitamin B12. In our stomach, LAB plays a beneficial role in checking disease-causing microbes.
  • Fermentation in Dough: The puffed-up appearance of dough (used for Dosa/Idli) is due to the production of CO2 gas by bacteria.
  • Baker’s Yeast: Saccharomyces cerevisiae is used for making bread.
  • Toddy: A traditional drink of Southern India made by fermenting sap from palms.
  • Cheese: * Large holes in Swiss Cheese: Due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii.
  • Roquefort Cheese: Ripened by growing specific fungi on them for a particular flavor.

Microbes in Industrial Products

For industrial scale, microbes are grown in very large vessels called Fermenters.

  • Beverages: Saccharomyces cerevisiae (also known as Brewer’s Yeast) is used for fermenting malted cereals and fruit juices to produce Ethanol.
    • Wine and Beer are produced without distillation.
    • Whisky, Brandy, and Rum are produced by distillation of the fermented broth.
  • Antibiotics: Chemical substances produced by some microbes which can kill or retard the growth of other (disease-causing) microbes.
  • Penicillin: The first antibiotic discovered by Alexander Fleming while working on Staphylococci bacteria. Its full potential was established later by Ernest Chain and Howard Florey.
  • Chemicals, Enzymes and other Bioactive Molecules:
    • Aspergillus niger (Fungus): Citric Acid.
    • Acetobacter aceti (Bacterium): Acetic Acid.
    • Clostridium butylicum (Bacterium): Butyric Acid.
    • Lactobacillus (Bacterium): Lactic Acid.
    • Lipases: Used in detergent formulations to remove oily stains from laundry.
    • Pectinases and Proteases: Used to clear bottled fruit juices.
    • Streptokinase: Produced by Streptococcus; used as a clot buster for removing clots from blood vessels of patients with myocardial infarction.
    • Cyclosporin A: Produced by the fungus Trichoderma polysporum; used as an immunosuppressive agent in organ-transplant patients.
    • Statins: Produced by the yeast Monascus purpureus; used as blood-cholesterol lowering agents (acts by competitively inhibiting the enzyme responsible for cholesterol synthesis).

Microbes in Sewage Treatment

Sewage contains large amounts of organic matter and microbes. Treatment is done in Sewage Treatment Plants (STPs).

  • Primary Treatment: Physical removal of particles (large and small) through filtration and sedimentation. All solids that settle form the primary sludge, and the supernatant forms the effluent.
  • Secondary Treatment (Biological Treatment):
    • Effluent is passed into large aeration tanks and agitated. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh-like structures).
    • Microbes consume organic matter, reducing the BOD (Biochemical Oxygen Demand).
    • BOD Definition: The amount of oxygen that would be consumed if all the organic matter in one liter of water were oxidized by bacteria. High BOD = High polluting potential.
    • Once BOD is reduced, effluent is passed into a settling tank where flocs sediment as activated sludge.
    • A small part of activated sludge is used as inoculum for the aeration tank; the rest is pumped into Anaerobic Sludge Digesters. Here, anaerobic bacteria digest the bacteria and fungi in the sludge, producing a mixture of gases (Methane, Hydrogen Sulphide, and CO2) which form Biogas.

Microbes in Production of Biogas

Biogas is a mixture of gases (predominantly methane) produced by microbial activity.

  • Methanogens: Bacteria which grow anaerobically on cellulosic material. A common example is Methanobacterium.
  • These are found in the rumen (a part of the stomach) of cattle. Thus, excreta (dung or Gobar) of cattle is rich in these bacteria.
  • Biogas Plant: Consists of a concrete tank (10-15 feet deep) where bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as gas is produced.
  • Technology of biogas production was developed in India mainly due to the efforts of IARI (Indian Agricultural Research Institute) and KVIC (Khadi and Village Industries Commission).

Microbes as Biocontrol Agents

Use of biological methods for controlling plant diseases and pests.

  • Ladybird and Dragonflies: Used to get rid of aphids and mosquitoes, respectively.
  • Bacillus thuringiensis (Bt): Used to control butterfly caterpillars. Available in sachets as dried spores which are mixed with water and sprayed on vulnerable plants.
  • Trichoderma: Free-living fungi found in the root ecosystems; effective biocontrol agents against several plant pathogens.
  • Baculoviruses (Genus: Nucleopolyhedrovirus): Pathogens that attack insects and other arthropods. They are species-specific, narrow spectrum insecticidal applications, and have no negative impacts on plants, mammals, or non-target insects.

Microbes as Biofertilisers

Organisms that enrich the nutrient quality of the soil.

  • Bacteria: Rhizobium in root nodules of leguminous plants (fix atmospheric nitrogen). Azotobacter and Azospirillum are free-living nitrogen fixers in soil.
  • Fungi: Form symbiotic associations with plants (Mycorrhiza). Many members of the genus Glomus form mycorrhiza. The fungus absorbs phosphorus from soil and passes it to the plant.
  • Cyanobacteria: Autotrophic microbes widely distributed in aquatic and terrestrial environments. Examples: Anabaena, Nostoc, Oscillatoria. In paddy fields, Cyanobacteria serve as an important biofertiliser. Blue-green algae also add organic matter to the soil.
  • Questions count: 10
  • Passing grade: 4
  • Time limit: 30 minutes
  • Number of allowed attempts: 5
Start Quiz
1.

Select all correct sentences. Explain the role of Lactic Acid Bacteria (LAB) in milk and its health benefits.

Microorganisms like Lactobacillus grow in milk and convert it into curd by producing acids.
These acids coagulate the milk and partially digest the milk proteins like casein.
The fermentation process by LAB significantly reduces the amount of Vitamin B12 in the curd.
Converting milk to curd improves its nutritional quality and digestibility for humans.
In the human stomach, LAB plays a very beneficial role in checking the growth of disease-causing microbes.
A small amount of curd added to fresh milk as an inoculum contains millions of these helpful bacteria.
2.

Describe the use of microbes in the production of industrial chemicals and enzymes.

Aspergillus niger is a bacterium used industrially to produce high yields of acetic acid.
Acetobacter aceti is the actual bacterium utilized for the large-scale production of acetic acid (vinegar).
Certain microbes are used to produce enzymes like lipases, which are added to laundry detergents.
Pectinases and proteases are commonly used in the food industry to clear bottled fruit juices.
Streptococcus produces streptokinase, which acts as a "clot buster" for heart patients.
These bioactive molecules are produced in massive vessels called fermenters to ensure high output.
3.

Discuss the process of Secondary Treatment in a Sewage Treatment Plant.  

The primary effluent is passed into large aeration tanks where it is constantly agitated and air is pumped in.
This allows the vigorous growth of useful aerobic microbes into mesh-like structures called flocs.
While growing, these microbes consume the major part of the organic matter in the effluent.
Once the BOD is significantly reduced, the effluent is passed into a settling tank where the bacterial flocs sediment.
This biological process is designed to increase the Biochemical Oxygen Demand (BOD) of the wastewater.
A small part of this activated sludge is pumped back into the aeration tank to serve as an inoculum.
4.

Explain the mechanism of Biogas production in a Biogas plant.  

Biogas is a mixture of gases, predominantly methane, produced by the anaerobic breakdown of organic matter.
These bacteria, such as Methanobacterium, are commonly found in the rumen of cattle.
In a biogas plant, a slurry of dung and water is fed into a concrete tank about 10 to 15 feet deep.
The bacteria involved, known as methanogens, grow aerobically on cellulosic materials like cow dung.
As the gas is produced due to microbial activity, a floating cover over the slurry keeps rising.
The produced biogas is then branched out through pipes to be used for cooking and lighting in nearby areas.
5.

Describe the role of microbes as biocontrol agents in agriculture.  

Biocontrol refers to the use of biological methods for controlling plant diseases and pests.
The ladybird beetle and dragonflies are useful for getting rid of aphids and mosquitoes respectively.
Trichoderma species are pathogenic bacteria that infect the roots of crops to stop fungal growth.
Bacillus thuringiensis (Bt) is used to control butterfly caterpillars without harming other insects.
Baculoviruses of the genus Nucleopolyhedrovirus are excellent for species-specific, narrow-spectrum insecticidal applications.
These methods reduce our dependence on toxic chemical pesticides and help maintain biodiversity.
6.

Discuss the importance of Biofertilisers in enriching soil fertility.  

Mycorrhiza is a parasitic relationship where fungi take phosphorus away from the plant roots.
Biofertilisers are organisms that enrich the nutrient quality of the soil through biological processes.
The main sources of biofertilisers are bacteria, fungi, and cyanobacteria.
Rhizobium forms a symbiotic association with leguminous plants to fix atmospheric nitrogen.
Cyanobacteria like Anabaena and Nostoc serve as important nitrogen fixers in paddy fields.
Using biofertilisers is an eco-friendly way to reduce the use of chemical fertilizers in farming.
7.

Explain the function of bioactive molecules: Cyclosporin A and Statins. 

Bioactive molecules are functional substances produced by microbes for specific medical uses.
Statins are molecules used to lower blood cholesterol levels in patients at risk of heart disease.
Statins function by competitively inhibiting the enzyme responsible for synthesizing cholesterol.
Cyclosporin A is produced by the yeast Monascus purpureus to help prevent blood clots.
It is actually used to prevent the immune system from rejecting organs in transplant patients.
Both of these molecules have revolutionized modern medicine by providing natural alternatives to synthetic drugs.
8.

How is Baker's Yeast used in the household food industry?  

The puffed-up appearance of dough used for making bread is a result of microbial activity.
This is achieved by adding Saccharomyces cerevisiae, commonly known as Baker's Yeast.
The carbon dioxide gas is trapped in the dough, causing it to shrink and become very dense.
The yeast ferments sugars present in the dough to produce ethanol and carbon dioxide.
Similar fermentation processes are used to prepare traditional southern Indian dishes like Idli and Dosa.
Toddy, a traditional drink, is also made by fermenting sap from palms using natural yeasts.
9.

Describe the discovery and potential of Antibiotics.  

Antibiotics are chemical substances produced by microbes that can kill or inhibit other disease-causing microbes.
Alexander Fleming discovered Penicillin by chance while working on Staphylococci bacteria.
Fleming immediately purified the mold and used it to cure thousands of soldiers during World War I. (incorrect - its full potential as an effective antibiotic was established later by Ernest Chain and Howard Florey for use in World War II)
He noticed a mold growing in an unwashed culture plate that prevented the bacteria from growing around it.
Its full potential as an effective antibiotic was later recognized by the Nobel Prize committee in 1945.
Today, antibiotics are essential for treating deadly diseases like plague, whooping cough, and diphtheria.
10.

Explain the role of Methanogens in the rumen of cattle.  

In the rumen, these bacteria help the cattle by breaking down proteins into simple sugars.
Cattle excreta, commonly known as gobar, is a primary source for the production of biogas.
This is because the dung is rich in methanogens, which are specialized anaerobic bacteria.
These bacteria are present in the rumen, a specific part of the stomach of cattle.
The breakdown of cellulose in the rumen is essential for the nutrition of the cattle.
This symbiotic relationship provides nutrition to the cattle and methane-rich waste for us.
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