Microbes in Human Welfare Chapter Notes | Biology Class 12 - NEET PDF Download

Introduction

Microorganisms, often viewed as harmful pathogens, actually play a crucial role in benefiting humanity. They are involved in various processes that enhance our daily lives, particularly in the production of household and industrial products.

In Household Products: 
Microbes are vital for fermentation, a process that transforms substances into different forms. For example, they are responsible for:

• Yogurt and Curd: Microorganisms like bacteria ferment milk to produce yogurt and curd, which are staple food items in many households.
• Cheese and Paneer: Bacteria and enzymes work together to ferment milk, leading to the production of cheese and paneer, popular ingredients in various cuisines.
• Dough Fermentation: Microbes are essential in fermenting dough used for making bread, idli, and dosa, contributing to the unique textures and flavors of these foods.

In Industrial Products: 
Microorganisms play a crucial role in various industrial processes, including:

• Production of Alcoholic Beverages: Microbes ferment sugars to produce alcoholic beverages like beer, wine, and spirits, showcasing their importance in the beverage industry.
• Antibiotic Production: Microorganisms are responsible for producing antibiotics like Penicillin, which are vital in combating infections and improving public health.
• Production of Chemicals, Enzymes, and Bioactive Molecules: Microbes synthesize various chemicals, enzymes, and bioactive molecules used in diverse applications, including pharmaceuticals, food processing, and biotechnology.

Microbes: Sewage Treatment and Biogas Production

• Sewage Treatment: Sewage treatment is essential for reducing pollution before discharging wastewater into the environment. This process primarily involves heterotrophic microbes found in sewage and occurs in two main stages: primary treatment and secondary treatment (or biological treatment). These stages significantly lower the biochemical oxygen demand (BOD) of the effluent, which measures the amount of oxygen consumed by bacteria to break down organic matter in water. A higher BOD indicates a greater potential for pollution. Therefore, sewage is treated until its BOD is sufficiently reduced to ensure safer discharge into the environment.

• Biogas Production: Microbes such as Methanobacterium, which thrive in anaerobic sludge, play a vital role in sewage treatment and are also found in the stomachs of ruminants. Cattle excreta, or gobar, is rich in bacteria, making it a valuable resource for biogas production, commonly known as gobar gas. This biogas can be utilized as a renewable energy source for cooking and heating.

• As Biocontrol Agents: Biocontrol involves using biological methods to manage plant pests and diseases instead of relying solely on chemical pesticides. This approach promotes a healthier ecosystem by encouraging natural predators and pests, reducing the need for harmful chemicals. Microbial biocontrol agents, such as Bacillus thuringiensis, are commonly used and can be applied as dry spores on plants to protect them from pests. Advances in genetic engineering have enabled scientists to insert genes from Bacillus thuringiensis into plants, making crops like Bt-cotton resistant to insect attacks. Baculoviruses from the genus Nucleopolyhedrovirus are also used as effective biological control agents.

Microbes in the Production of Biogas and Biocontrol Agents

• Biogas is a renewable energy source produced by microorganisms breaking down organic matter without oxygen. This process generates a mixture of gases, primarily methane, along with carbon dioxide and hydrogen. The key players in this process are methanogenic bacteria, such as Methanobacterium, which thrive on cellulosic materials.
• Biogas plants often use cattle excreta, or gobar, as a rich source of these methanogens. The technology for biogas production was developed in India by the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).
• A typical biogas plant consists of a concrete tank where organic waste and dung slurry are mixed. A floating cover on top of the digester rises as gas accumulates, and this gas is channeled through an outlet pipe for use. The leftover slurry is expelled through another outlet and can be used as fertilizer. These plants are commonly found in rural areas with easy access to large quantities of cattle dung.

Microbes in the Production of Biogas:

• Biogas is a renewable energy source produced by microorganisms breaking down organic matter in the absence of oxygen. The primary gases in biogas are methane, carbon dioxide (CO₂), and hydrogen (H₂).
• The bacteria responsible for biogas production are known as methanogens, with examples like Methanobacterium that thrive on cellulosic materials.
• In biogas plants, cattle excreta, or gobar, serves as a rich source of methanogens for biogas production.
• The technology for biogas generation was pioneered in India by the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).
• A typical biogas plant includes a concrete tank where organic waste and dung slurry are collected. A floating cover sits atop the digester, moving upward as gas accumulates.
• The accumulated gas is channeled through an outlet pipe for use, while the leftover slurry is expelled through another outlet and can be used as fertilizer.
• Biogas plants are often constructed in rural areas, where there is easy access to large quantities of cattle dung.

Biocontrol Agents:

• Microbes play a crucial role in the production of biocontrol agents, which are used to manage pests and diseases in agriculture.
• Examples of biocontrol agents include Trichoderma and Bacillus thuringiensis(Bt).
• Trichoderma is a fungus that helps control soil-borne diseases by outcompeting harmful pathogens.
• Bacillus thuringiensis(Bt) is a bacterium that produces proteins toxic to certain insect pests, making it an effective biopesticide.
• These biocontrol agents are environmentally friendly alternatives to chemical pesticides, promoting sustainable agriculture.

Microbes as Biocontrol Agents

Examples of Microbial Biocontrol Agents:

• Bacillus thuringiensis: This soil-dwelling bacterium is used to manage caterpillar infestations on crops such as brassicas (e.g., cabbage, broccoli) and fruit trees. Bacillus thuringiensis produces toxins that are specifically harmful to certain insect larvae, making it an effective biocontrol agent.
• Trichoderma: This beneficial fungus naturally occurs in the soil and colonizes plant root systems. Trichoderma helps control various plant pathogens by outcompeting them for resources and producing substances that are toxic to the pathogens. It is commonly used to protect crops from soil-borne diseases.
• Baculoviruses: These are viruses that specifically target insect pests. For example, baculoviruses from the genus Nucleopolyhedrovirus are used to control specific insect pests like caterpillars. These viruses are highly specific to their host insects, making them ideal for narrow-spectrum insecticidal applications. This specificity helps reduce the impact on non-target organisms and supports sustainable agricultural practices.

By using these microbial biocontrol agents, farmers can effectively manage pests and diseases while promoting environmental sustainability and reducing reliance on chemical pesticides.

Microbes as Biofertilizers

• Biofertilizers are natural substances that contain living microorganisms, which promote the growth of plants by increasing the supply or availability of primary nutrients to the host plant. These beneficial organisms play a crucial role in enhancing the nutrient quality of the soil, thereby helping plants grow healthier and stronger. Biofertilizers mainly include bacteria, fungi, and cyanobacteria, each contributing uniquely to soil fertility and plant nutrition.
• For example, Rhizobium bacteria form a symbiotic relationship with leguminous plants, fixing atmospheric nitrogen into a form that plants can use. Similarly, mycorrhizal fungi help plants absorb phosphorus and improve their resistance to diseases. By using these natural organisms, farmers can improve soil health, promote sustainable agriculture, and reduce reliance on chemical fertilizers.

Rhizobium Bacteria and Nitrogen Fixation:

• Rhizobium bacteria play a vital role in enhancing soil nitrogen levels by forming symbiotic relationships with leguminous plants (such as peas, beans, and lentils).
• These bacteria inhabit root nodules on the plants, where they convert atmospheric nitrogen into a form that plants can use for their growth and metabolic processes.
• This process is crucial because nitrogen is an essential nutrient that supports various plant functions, including protein synthesis and chlorophyll production.
• For instance, when a farmer plants soybeans, the Rhizobium bacteria associated with the soybean roots help fix nitrogen from the air, enriching the soil and providing the necessary nutrients for the plant's growth.

Free-living Nitrogen-fixing Bacteria:

• Azotobacter and Azospirillum are examples of free-living bacteria that reside in the soil and contribute to nitrogen fixation.
• These bacteria convert atmospheric nitrogen into forms that are available for plant uptake, thus enhancing soil fertility.
• For example, Azotobacter can be found in various soil types, where it fixes nitrogen and makes it accessible to plants, improving their overall health and productivity.

Mycorrhizal Fungi and Nutrient Absorption:

• Mycorrhizal fungi, particularly those from the Glomus genus, form symbiotic relationships with angiosperm plants.
• These fungi colonize plant roots and extend their hyphae into the soil, increasing the surface area for nutrient absorption.
• Mycorrhizal fungi are especially important for the uptake of phosphorus, a crucial nutrient for plant energy transfer and photosynthesis.
• Additionally, this symbiosis offers plants increased resistance to root-borne pathogens, as well as enhanced tolerance to environmental stresses like salinity and drought.
• For instance, when a farmer plants corn, mycorrhizal fungi associated with the corn roots help absorb phosphorus from the soil, promoting healthy growth and improving the plant's ability to withstand drought conditions.

Cyanobacteria as Biofertilizers:

• Cyanobacteria, such as Nostoc and Anabaena, are autotrophic microbes that play a significant role in enhancing soil fertility, particularly in paddy fields.
• These organisms fix atmospheric nitrogen and contribute organic matter to the soil, enriching it further.
• For example, in paddy fields, cyanobacteria not only help in nitrogen fixation but also improve soil structure and fertility by adding organic matter.
• This process is essential for maintaining soil health and supporting sustainable agricultural practices.

Benefits of Using Microbes as Biofertilizers:

• Utilizing microbes as biofertilizers helps improve soil health naturally by enhancing its nutrient content and overall fertility.
• This approach promotes sustainable agriculture by reducing the reliance on chemical fertilizers, which can have adverse effects on the environment and soil health.
• Moreover, biofertilizers contribute to increased crop yields and improved plant health, supporting the overall productivity of agricultural systems.
• For instance, a farmer using mycorrhizal fungi and cyanobacteria in their paddy fields may observe healthier plants, higher yields, and reduced need for chemical inputs, leading to a more sustainable farming practice.