Role and Applications of Microorganisms

MCB 102: Introductory Microbiology

Role and Applications of Microorganisms

This lecture explores the diverse and crucial roles of microorganisms in various aspects of life, including medicine, agriculture, the environment, biotechnology, food, and industry.

Learning Objectives & Roadmap

By the end of this lecture, you should be able to:

• Describe at least three applications of microorganisms in each of the six key areas.
• Identify common microorganisms associated with each application.
• Explain, in simple terms, the principle behind each application.

What Are Microorganisms?

• Microorganisms (microbes): Living organisms too small to be seen with the naked eye.
• Characteristics: Most are harmless or beneficial; only a small fraction cause disease.
• Ubiquity: Found everywhere – soil, water, air, food, and inside our bodies.

Types of Microorganisms: Bacteria, Archaea, Fungi, Protozoa, Algae, Viruses.

Life on Earth, as we know it, would not be possible without microorganisms.

Applications in Medicine

1. Antibiotics & Vaccines

• Antibiotics: Substances produced by microbes that kill or inhibit other microbes.
  • Examples:
    • Penicillin: From *Penicillium notatum* (mold). Discovered by Alexander Fleming in 1928, it launched the antibiotic era.
    • Streptomycin: From *Streptomyces griseus* (bacterium).
    • Tetracycline: From *Streptomyces aureofaciens*.
    • Other examples from detailed list: Polymyxin B (*Bacillus polymyxa*), Neomycin (*Streptomyces fradiae*), Gentamicin (*Micromonospora purpurea*), Vancomycin (*Amycolatopsis orientalis*), Rifamycin (*Amycolatopsis mediterranei*), Erythromycin (*Saccharopolyspora erythraea*), Kanamycin (*Streptomyces kanamyceticus*).
• Vaccines: Stimulate the immune system to recognize a pathogen without causing disease.
  • Types:
    • Live attenuated: Weakened pathogen (e.g., oral polio, measles).
    • Inactivated: Killed whole pathogen (e.g., some flu vaccines).
    • Subunit/recombinant: Engineered yeast produces pathogen protein (e.g., hepatitis B vaccine).

2. Diagnostics, Therapeutics & Probiotics

• Diagnostic Microbiology:
  • Culturing samples to identify pathogens.
  • Enzyme-based test kits.
  • Monoclonal antibody rapid tests (e.g., malaria, COVID-19).
• Therapeutic Proteins:
  • Genetically engineered *E. coli* or yeast produce important proteins like insulin, growth hormone, and interferons for treating human diseases.
• Probiotics:
  • Live beneficial microbes (e.g., *Lactobacillus*, *Bifidobacterium*) that restore healthy gut microbiota and aid digestion.

Applications in Agriculture

Key idea: Microbes reduce reliance on chemical fertilizers and pesticides, thereby supporting more sustainable agriculture.

1. Nitrogen Fixation & Biofertilizers

• Rhizobium: Symbiotic nitrogen fixer in legume root nodules.
• Azotobacter / Azospirillum: Free-living nitrogen fixers in soil.
• Cyanobacteria: Fix nitrogen in rice paddies (e.g., *Anabaena*).
• Mycorrhizal fungi: Improve phosphorus and water uptake for plants.

2. Biopesticides & Soil Health

• Bacillus thuringiensis (Bt): Natural insect toxin; basis of Bt crops (genetically modified plants producing Bt toxin).
• Trichoderma: Fungal biocontrol agent against plant pathogens.
• Decomposers: Bacteria and fungi recycle nutrients back into the soil.
• Silage: Lactic acid bacteria preserve livestock fodder through fermentation.

Applications in the Environment

1. Biogeochemical Cycling

• Microorganisms drive essential cycles of carbon, nitrogen, sulfur, and phosphorus (e.g., *Nitrosomonas*, *Nitrobacter* in the nitrogen cycle).

2. Decomposition

• Saprophytic bacteria and fungi break down dead organic matter, thereby recycling nutrients in ecosystems.

3. Bioremediation

• Microbes like *Pseudomonas* degrade pollutants such as oil spills, pesticides, and heavy metals, cleaning up contaminated environments.

4. Wastewater & Biogas

• Microbes are used to treat sewage (e.g., activated sludge process) and produce methane-rich biogas, a renewable energy source.

Applications in Biotechnology

1. Recombinant DNA Technology

• *E. coli* and yeast are widely used as host organisms to express foreign genes, leading to the production of therapeutic proteins like insulin, human growth hormone, and various vaccines.
• Process Overview: Involves removing plasmid DNA from a bacterium, generating and selecting desired DNA fragments, cutting the plasmid and inserting the DNA fragment to create recombinant DNA, and finally inserting this recombinant DNA into host cells for expression.

2. Industrial & Diagnostic Enzymes

• Restriction enzymes: Essential tools for cutting DNA at specific sites.
• Heat-stable Taq polymerase: From *Thermus aquaticus*, crucial for Polymerase Chain Reaction (PCR) and molecular biology applications.
• Other Industrial Enzymes (detailed):
  • Amylase: Starch hydrolysis in baking, brewing, detergents (*Bacillus subtilis*, *Aspergillus oryzae*).
  • Protease: Stain removal, meat tenderizing, cheese making (*Bacillus licheniformis*).
  • Cellulase: Bio-stonewashing, paper processing, biofuels (*Trichoderma reesei*).
  • Lipase: Detergents, flavor development, biodiesel production (*Candida antarctica*, *Aspergillus niger*).
  • Pectinase: Fruit juice clarification (*Aspergillus niger*).
  • Glucose oxidase: Food preservation, glucose biosensors (*Aspergillus niger*).
  • Rennin (Chymosin): Cheese manufacturing (*Aspergillus niger*, *Kluyveromyces lactis*).
  • Xylanase: Paper pulp bleaching, animal feed additive (*Trichoderma reesei*).
  • Streptokinase: Clot-dissolving agent (*Streptococcus species*).
  • Penicillin acylase: Production of semi-synthetic penicillins (*E. coli*).
  • Glucose isomerase: Conversion of glucose to fructose (*Streptomyces species*).
  • Catalase: Removal of hydrogen peroxide in food processing (*Aspergillus niger*).
  • Asparaginase: Treatment of acute lymphoblastic leukemia, acrylamide reduction in fried foods (*E. coli*).
  • Invertase: Confectionery industry (*Saccharomyces cerevisiae*).

3. Genetically Modified Crops

• *Agrobacterium tumefaciens* naturally transfers genes into plants, making it a key tool for developing pest- and herbicide-resistant crops.
• Process Overview: *Agrobacterium tumefaciens* contains a Ti plasmid. A desired gene (e.g., for pest resistance) is inserted into this plasmid. The bacterium then transfers this modified T-DNA into the plant cell's genome, resulting in a plant with new traits.

4. Organic Acids (Biotechnology Production)

• Microorganisms produce various organic acids used in food, pharmaceuticals, and industry.
  • Citric Acid: *Aspergillus niger*. Used as an acidulant, preservative, flavoring, chelating agent.
  • Lactic Acid: *Lactobacillus delbrueckii*, *Lactobacillus bulgaricus*. Used in food preservation, dairy products, biodegradable plastics (PLA).
  • Acetic Acid: *Acetobacter aceti*, *Gluconobacter species*. Vinegar production, food preservative.
  • Fumaric Acid: *Rhizopus oryzae*. Food acidulant, production of unsaturated polyester resins.
  • Propionic Acid: *Propionibacterium freudenreichii*. Food and feed preservative, Swiss cheese production.
  • Malic Acid: *Aspergillus flavus*. Food acidulant, wine making, pharmaceuticals.
  • Kojic Acid: *Aspergillus oryzae*. Skin-lightening agent, antioxidant.

Applications in Food

1. Food Products & Processes

• Bread: *Saccharomyces cerevisiae* (yeast) – alcoholic fermentation produces CO2 that raises dough.
• Yogurt: *Lactobacillus spp*, *Streptococcus thermophilus* – lactic acid fermentation of milk.
• Cheese: Lactic acid bacteria, *Penicillium* molds – fermentation & ripening of curdled milk.
• Beer / Wine: *Saccharomyces cerevisiae* – alcoholic fermentation of grain/grape sugars.
• Vinegar: *Acetobacter* species – oxidizes ethanol to acetic acid.

2. Other Roles in Food

• Preservation: Lactic acid bacteria lower pH, inhibiting spoilage microbes (e.g., pickles, sauerkraut).
• Single-cell protein: Yeast, bacteria, and algae (e.g., *Spirulina*) grown as protein-rich food/feed.
• Additives: Microbes produce vitamins (e.g., B12), MSG, and various flavor compounds.

Applications in Industry

1. Organic Acids

• Citric acid: (*Aspergillus niger*) – used in food, plastics, and pharmaceuticals.
• Lactic acid: Used in food, plastics, and pharmaceuticals.
• Acetic acid: Used in food, plastics, and pharmaceuticals.

2. Alcohols & Solvents

• Ethanol: (*Saccharomyces*) – used as fuel and in various industries.
• Acetone-butanol: (*Clostridium*) – used as fuel and in various industries.

3. Industrial Enzymes

• Amylases, proteases, lipases, cellulases: Used in detergents, textiles, and paper manufacturing.

4. Biofuels & Bioplastics

• Bioethanol: Produced from biomass by microorganisms.
• Biogas: Methane-rich gas produced from organic waste by anaerobic digestion.
• Biosurfactants: Microbially produced detergents.
• Biodegradable PHA bioplastics: Polyhydroxyalkanoates produced by bacteria as energy storage, offering an eco-friendly alternative to conventional plastics.