Detailed Notes -2- Chapter 8- Microbes In Human Welfare

8.4 MICROBES IN PRODUCTION OF BIOGAS

1. Biogas Production:

   • Biogas is a mixture of gases, predominantly methane, produced by microbial activity.
   • Methanogens are bacteria that grow anaerobically on cellulosic material and produce methane along with carbon dioxide and hydrogen.
   • Methanogens, like Methanobacterium, are commonly found in anaerobic sludge during sewage treatment and in the rumen of cattle.

2. Role of Methanogens:

   • In the rumen of cattle, methanogens help in the breakdown of cellulose, playing a crucial role in the nutrition of cattle.
   • Human beings cannot digest cellulose present in food.

3. Biogas Generation from Cattle Dung:

   • Cattle dung, rich in methanogens, can be used for the generation of biogas, commonly known as gobar gas.
   • Biogas plants typically consist of a concrete tank where bio-wastes are collected, and a slurry of dung is fed.
   • A floating cover over the slurry collects the gas produced by microbial activity.
   • The biogas produced is then used for cooking and lighting in nearby houses.
   • The spent slurry can be used as fertilizer.

4. Biogas Plant Technology:

   • Biogas production technology was developed in India mainly through the efforts of organizations like the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).

5. Role in Rural Areas:

   • Biogas plants are more commonly built in rural areas where cattle dung is readily available and used for various purposes.
   • The technology helps in providing renewable energy and addressing energy needs in rural areas.

6. Educational Opportunities:

   • Schools located in or near villages can explore nearby biogas plants to learn more about the technology and its management from local experts.

8.5 MICROBES AS BIOCONTROL AGENTS

1. Introduction to Biocontrol:

   • Biocontrol involves the use of biological methods to control plant diseases and pests, as opposed to chemical methods.
   • Chemical insecticides and pesticides are toxic, harmful to humans, animals, and the environment, and contribute to pollution.

2. Biological Control in Agriculture:

   • Organic farming emphasizes biodiversity and natural predation to manage pests within a balanced ecosystem.
   • Instead of eradicating pests, organic farming aims to maintain them at manageable levels through natural checks and balances.
   • Understanding the interactions between different organisms in the ecosystem is crucial for effective biocontrol.

3. Examples of Biocontrol Agents:

   • Ladybirds and dragonflies are natural predators that help control aphids and mosquitoes, respectively.
   • Microbial biocontrol agents, like Bacillus thuringiensis (Bt), are used to control butterfly caterpillars by introducing dried spores mixed with water, which release toxins in the larvae’s gut, killing them without harming other insects.
   • Genetic engineering has enabled the incorporation of Bt toxin genes into plants like Bt-cotton, making them resistant to insect pests.

4. Use of Fungi in Biocontrol:

   • Trichoderma species, common in root ecosystems, are effective biocontrol agents against several plant pathogens.

5. Baculoviruses as Biocontrol Agents:

   • Baculoviruses, particularly those in the genus Nucleopolyhedrovirus, attack insects and other arthropods, offering species-specific, narrow-spectrum insecticidal applications.
   • These viruses have minimal negative impacts on non-target organisms, making them suitable for integrated pest management (IPM) programs and ecologically sensitive areas.

8.6 MICROBES AS BIOFERTILISERS

1. Introduction to Biofertilizers:

   • Biofertilizers are organisms that enrich the nutrient quality of the soil and are considered an alternative to chemical fertilizers, aiming to promote sustainable agriculture.
   • The main sources of biofertilizers are bacteria, fungi, and cyanobacteria.

2. Bacterial Biofertilizers:

   • Bacteria such as Rhizobium form symbiotic associations with leguminous plants, fixing atmospheric nitrogen into organic forms that are utilized by the plants as nutrients.
   • Other nitrogen-fixing bacteria like Azospirillum and Azotobacter enrich the nitrogen content of the soil by fixing atmospheric nitrogen while free-living in the soil.

3. Fungal Biofertilizers:

   • Fungi, particularly members of the genus Glomus, form mycorrhizal associations with plants, helping in the absorption of phosphorus from the soil and passing it to the plant.
   • Mycorrhizal associations provide additional benefits to plants, such as resistance to root-borne pathogens, tolerance to salinity and drought, and overall increased plant growth and development.

4. Advantages of Fungal Associations:

   • The fungus benefits from the association by receiving organic compounds and sugars from the plant, aiding its own growth and survival.

5. Cyanobacterial Biofertilizers:

   • Cyanobacteria, including Anabaena, Nostoc, and Oscillatoria, are autotrophic microbes capable of fixing atmospheric nitrogen.
   • In paddy fields, cyanobacteria serve as important biofertilizers, enriching the soil with nitrogen.
   • Blue-green algae, a type of cyanobacteria, also contribute to soil fertility by adding organic matter.

6. Commercial Availability and Usage:

   • Many biofertilizers are commercially available in the market, and farmers use them regularly to replenish soil nutrients and reduce dependence on chemical fertilizers.