Comprehensive theory, key formulas, diagrams, and memory aids for Microbes in Human Welfare.
Microorganisms, or microbes, are organisms that are too small to be seen with the naked eye. They include bacteria, fungi, protozoa, viruses, and certain algae. Although some microbes cause diseases, the vast majority are beneficial to humans in countless ways. This chapter explores the diverse applications of microbes in human welfare, from the production of food and beverages to the generation of industrial products, the treatment of sewage, the production of biogas, and the improvement of agricultural productivity.
The chapter demonstrates that microbes have been used by humans for thousands of years, often without understanding the underlying biology. The production of curd, bread, cheese, and alcoholic beverages relies on microbes. Modern biotechnology has further expanded the use of microbes in the production of antibiotics, vitamins, enzymes, organic acids and other valuable products. Microbes also play a vital role in environmental management, such as sewage treatment and biogas production, and in agriculture as biofertilisers and biocontrol agents. Understanding the beneficial roles of microbes helps us appreciate their importance in maintaining a sustainable and healthy environment.
Microbes are used in the production of many household products, especially in the food industry.
Microbes are used on a large scale in industrial fermenters to produce valuable products such as organic acids, alcohols, antibiotics, vitamins and enzymes.
Antibiotics are chemical substances produced by microorganisms that can kill or inhibit the growth of other microorganisms. The first antibiotic discovered was penicillin, produced by the mould Penicillium notatum, discovered by Alexander Fleming in 1928. Antibiotics have revolutionised medicine and saved millions of lives. Other important antibiotics include streptomycin (from Streptomyces griseus) and erythromycin. Antibiotics are now produced in large quantities in industrial fermenters.
Sewage is the municipal waste water that contains large amounts of organic matter and microbes. The treatment of sewage is essential to prevent the pollution of water bodies and the spread of disease. Microbes play a central role in sewage treatment.
BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. The sewage is considered treated when the BOD of the effluent is significantly reduced, because the organic matter has been consumed by the aerobic microbes. A high BOD indicates high organic pollution; a low BOD indicates that the organic matter has been degraded.
Biogas is a mixture of gases, primarily methane and carbon dioxide, produced by the microbial fermentation of organic matter in the absence of oxygen. The bacteria that produce biogas are called methanogens. The most common methanogen is Methanobacterium, which is found in the rumen (stomach) of cattle and in the anaerobic sludge of sewage treatment plants.
In gobar gas plants (cattle dung gas plants), cattle dung is mixed with water and introduced into a biogas plant. The slurry of dung provides the food for the methanogens. In the absence of oxygen, the methanogens ferment the organic matter to produce biogas. The biogas is used as a source of energy for cooking and lighting. The spent slurry is used as manure because it is rich in nitrogen and phosphorus. Biogas production is a renewable and environment-friendly source of energy and also helps in the disposal of animal waste.
Biocontrol is the use of biological methods to control plant pests and diseases, as an alternative to chemical pesticides, which are harmful to the environment and human health. - Bacillus thuringiensis (Bt): This bacterium is used to control insect pests. It produces a protein (crystal toxin) that is lethal to certain insect larvae. Bt cotton is a genetically modified crop that contains the Bt toxin gene. - Trichoderma: This fungus is used as a biocontrol agent against several plant pathogens, especially soil-borne diseases. - Baculoviruses: These are viruses that attack insects and other arthropods. They are species specific and are used in biological pest management.
Biofertilisers are organisms that enrich the nutrient quality of the soil, mainly by fixing atmospheric nitrogen or solubilising phosphorus. - Rhizobium: A symbiotic nitrogen-fixing bacterium that lives in the root nodules of leguminous plants and fixes atmospheric nitrogen into a form the plant can use. - Azospirillum and Azotobacter: Free-living nitrogen-fixing bacteria that enrich the soil with nitrogen. - Blue-green algae (cyanobacteria): Like Anabaena and Nostoc, which are important nitrogen fixers, especially in paddy fields. They also add organic matter to the soil. - Mycorrhiza: A symbiotic association of fungi with plant roots. The fungus helps the plant absorb phosphorus and other nutrients from the soil, and the plant provides the fungus with carbohydrates. Mycorrhiza helps in the uptake of phosphorus and increases the tolerance of plants to stress.
| Product | Microorganism | Type |
|---|---|---|
| Acetic acid (vinegar) | Acetobacter aceti | Bacterium |
| Lactic acid | Lactobacillus | Bacterium |
| Citric acid | Aspergillus niger | Fungus |
| Alcohol | Saccharomyces cerevisiae | Yeast |
| Penicillin | Penicillium notatum | Fungus |
| Streptokinase | Streptococcus | Bacterium |
| Application | Microorganism |
|---|---|
| Curd | Lactobacillus |
| Roquefort cheese | Penicillium roqueforti |
| Bread (dough rising) | Saccharomyces cerevisiae |
| Nitrogen fixation (legumes) | Rhizobium |
| Nitrogen fixation (paddy) | Anabaena, Nostoc |
| Biocontrol of pests | Bacillus thuringiensis |
| Phosphorus uptake | Mycorrhiza |
| Term | Meaning |
|---|---|
| BOD | Oxygen consumed by bacteria to oxidise organic matter in one litre of water |
| Methanogens | Anaerobic bacteria producing methane, e.g., Methanobacterium |
| Flocs | Masses of bacteria and fungal filaments in aeration tank |
| Primary sludge | Settled solids from primary treatment |
flowchart TD
A["MICROBES IN HUMAN WELFARE"] --> B["Household products"]
A --> C["Industrial products"]
A --> D["Sewage treatment"]
A --> E["Biogas production"]
A --> F["Biocontrol and biofertilisers"]
B --> B1["Curd: Lactobacillus"]
B --> B2["Bread and alcohol: Saccharomyces"]
C --> C1["Acids: Acetobacter, Aspergillus niger"]
C --> C2["Antibiotics: penicillin"]
C --> C3["Enzymes: lipase, streptokinase"]
D --> D1["Primary and secondary treatment"]
D --> D2["BOD and flocs"]
E --> E1["Methanobacterium in gobar gas plants"]
F --> F1["Bt, Trichoderma, baculoviruses"]
F --> F2["Rhizobium, cyanobacteria, mycorrhiza"]
Microbes in human welfare reveal the enormous beneficial potential of organisms that are often only associated with disease. From the everyday production of curd, bread and cheese to the industrial manufacture of acids, enzymes, antibiotics and vitamins, microbes are indispensable partners of human civilisation. Their role in sewage treatment, where they degrade organic waste and reduce BOD, and in biogas production, where methanogens convert animal waste into clean energy, demonstrates their environmental importance. In agriculture, biocontrol agents and biofertilisers offer sustainable alternatives to harmful chemicals, enriching the soil and controlling pests naturally. The chapter thus shifts the perspective from microbes as pathogens to microbes as engines of food production, industry, sanitation and sustainable agriculture, laying a foundation for the biotechnology chapters that harness these microscopic organisms through genetic engineering.