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BIOTECHNOLOGICAL ASPECTS OF MICROBIAL ECOLOGY

Biopesticides

  • Definition:
    • Biopesticides, also known as biological pesticides, are chemicals made from natural organisms or substances used to control or suppress agricultural pests, weeds, and disease-causing agents by specific biological effects.
    • According to the US Environment Protection Agency (EPA), “Biopesticides are certain types of pesticides derived from natural materials such as animals, plants, bacteria, and certain minerals.”
Types of Biopesticides

  • Classification Based on Source/Origin of Extraction:

    • Biopesticides can be classified into three main classes:

    A. Microbial Pesticides

    • Derived from microorganisms, including:
      • Bacteria
      • Viruses
      • Fungi
      • Protozoa
      • Entomopathogenic nematodes
    • Modes of Action:
      • Causing disease in pests
      • Creating competition for food and space
      • Producing toxic metabolites
    • Examples of Microbial Pesticides:
      • Bacterial Biopesticides:
        • Commonly used to control insects, some target bacteria and fungi as well.
        • Notable species:
        • Bacillus thuringiensis (Bt) Berliner - extensively studied and commercially significant.
        • Other species include Bacillus subtilis, Pseudomonas fluorescens, Agrobacterium radiobacter, etc.
      • Viral Biopesticides:
        • Families that infect insects, particularly family Baculoviridae, which is used as pesticides.
        • Mechanism: Infect insects through ingestion; viruses release particles leading to infection and death over days, with subsequent release into the environment.
      • Fungal Biopesticides:
        • Control insects and also target fungi and bacteria.
        • Unlike bacterial or viral, they can penetrate through the cuticle.
        • Examples: Beauveria bassiana, Metarhizium anisopliae, Trichoderma viride, Paecilomyces farinosus, Verticillium lecanii.

    B. Biochemical Pesticides

    • Plant Extracts (Botanicals):
      • Derived from plants and essential oils, including secondary metabolites (e.g., steroids, alkaloids, phenolics).
      • Functions: Repellents, growth regulators, antifeedants, inhibiting respiration, causing metabolic dysfunction.
      • Examples: Neem (from Azadirachta indica), Nicotine (from Nicotiana species), Pyrethrum (from Dalmatia pyrethrum), Ryanodine (from Ryania speciosa).
    • Semiochemicals:
      • Chemicals that cause behavioral/physiological changes in organisms of the same/different species.
      • Applications: Mass trapping, lure and kill, mating disruption, push-pull systems, activating plant defenses.
    • Growth Regulators:
      • Insect growth regulators (IGRs) which interfere with insect growth and development.
      • Include Juvenile hormone analogues (JHAs), ecdysteroids analogues, chitin synthesis inhibitors (CSIs).

    C. Plant Incorporated Protectants (PIPs)

    • Derived from genetically modified (GM) plants incorporating genetic material exhibiting pesticide activity.
    • Most notable example: Bt crops, incorporating Cry proteins from Bacillus thuringiensis.
    • Consumer resistance in some countries leads to debate over classification as biopesticides.
Advantages of Biopesticides
  1. Environmentally friendly, low toxicity to humans and organisms.
  2. Target specificity reduces harm to beneficial organisms.
  3. Lower risk of pest resistance.
  4. Biodegradable, reducing environmental exposure risks.
  5. Compatible with Integrated Pest Management (IPM) programs.
Disadvantages of Biopesticides
  1. Short shelf life limits usability.
  2. Limited effectiveness under specific environmental conditions.
  3. Target species limitation restricts pest range control.
  4. Application may be difficult and confusing for farmers.
  5. Regulatory approval can be lengthy and production costs can be high.

Biofertilizers

  • Definition: Natural formulations containing living microorganisms (beneficial bacteria, fungi, and algae) that enrich soil, promoting plant health and growth. They enhance nutrient availability, especially nitrogen, phosphorus, and potassium, instead of merely feeding.
Advantages Over Chemical Fertilizers
  • Cost-effectiveness
  • Reduced plant disease risk
  • Minimization of health risks for consumers of food grown with chemical fertilizers.
  • Non-polluting qualities.
Need for Biofertilizers
  • Restoration of soil fertility is vital due to chemical fertilizers causing degradation and affecting crop yield. Enhances soil's water holding capacity and contributes essential nutrients like nitrogen, vitamins, and proteins.
Microorganisms Used as Biofertilizers
  • Examples include:
    • Rhizobium
    • Azotobacter
    • Azospirilium
Mechanism of Action
  • Biofertilizers aid in plant growth by:
    • Trapping atmospheric nitrogen and converting it to ammonia.
    • Converting insoluble phosphates into soluble forms conducive for plants.
Main Sources of Biofertilizers
  • Bacteria, cyanobacteria, and fungi.
Key Characteristics of Rhizobium
  • Important nitrogen-fixing bacteria forming symbiotic associations with leguminous plants in root nodules. Converts atmospheric nitrogen to ammonia, enhancing plant growth.
Benefits of Biofertilizers
  1. Enhances Soil Fertility: Through nitrogen fixation, phosphate solubilization, micronutrient mobilization, and maintaining biodiversity.
  2. Improves Growth and Yield: Natural growth-promoting hormones (auxins, gibberellins, cytokinins) produced, enhancing root growth and nutrient uptake.
  3. Eco-Friendly: Reduce pesticide runoff, lower greenhouse gas emissions, and prevent soil toxicity.
  4. Cost-Effective for Farmers: Reduced need for synthetic inputs, thus lowering expenses while maintaining yields.
  5. Improves Soil Structure and Water Retention: Increased microbial activity aids soil aggregation and porosity, particularly beneficial in drought-prone areas.
  6. Supports Organic Farming: Compatibility with organic inputs without disrupting certification standards.

Bioplastics

  • Definition: Bioplastics are materials that are either bio-based (derived from renewable resources) or biodegradable (capable of breaking down through microbial action) or both.
Key Characteristics of Bioplastics
  1. Bio-based Content: They use biomass such as corn, sugarcane, or cellulose, instead of petroleum resources.
  2. Biodegradability: Many, yet not all, bioplastics decompose into harmless elements like water and carbon dioxide.
Types of Bioplastics
  • Major Categories:
    • Polylactic Acid (PLA):
    • Derived from corn syrup.
    • Characteristics: Rigid, transparent, compostable under industrial conditions. Used in food packaging and 3D printing.
    • Polyhydroxyalkanoates (PHA):
    • Produced by bacteria from sugars or oils. Fully biodegradable in natural environments.
    • Applications include sutures and packaging.
    • Bio-PET (Polyethylene Terephthalate):
    • Made from plants but not biodegradable. Used for beverage bottles.
    • Starch Blends: Flexible materials combining starch with other biodegradable polymers used in bags and packaging films.
Production Process of Bioplastics
  1. Collection of agricultural crops or residues as feedstock.
  2. Extraction of starches and sugars.
  3. Fermentation of sugars by microorganisms producing building blocks like lactic acid.
  4. Polymerization of building blocks into bioplastics.
  5. Processing the resin into products such as films and packaging.
Addressing Plastic Waste
  • Explanation of the challenges of traditional plastic disposal, where 43% ends up in landfills or oceans.
  • Bioplastics serve as an environmentally friendlier alternative, designed for quicker degradation.