Comprehensive Guide to Microorganisms: Friend and Foe

Introduction to Microorganisms

• The Unseen World: The Earth hosts a vast number of living organisms, many of which are too small to be seen with the naked eye. These are found in water, air, solid rocks, and even inside the human body.

• Tune In Scenario: Eeshan noticed white spots on his shoes after they were stored in a cupboard for four months following the monsoon break. These spots were caused by microorganisms that grew due to moisture and organic matter in the shoes.

• Definition: Tiny living organisms that can only be seen through a system of lenses or a microscope are called microorganisms or microbes.

• Microbiology: The scientific study of microorganisms is known as microbiology.

Fundamentals of Microbes

• Size: The average size of a microorganism is approximately $1\,\mu\text{m}$ (micrometre), where $1\,\mu = 10\text{ metres}$ (as per transcript notation). They are often unicellular, but some can be multicellular.

• Habitats: Microorganisms are highly resilient and can survive in harsh environments, including:

  • Deserts and polar caps.

  • Hot springs.

  • Inside the bodies of animals and plants.

  • Soil, air, and water.

• History of Discovery:

  • Invention of the Microscope: The early $17^{th}$ century allowed for the observation of these organisms.

  • Antonie van Leeuwenhoek: A Dutch businessman and scientist known as the "Father of Microbiology." He was among the first to see microbes in rainwater using a simple microscope of his design.

  • Robert Hooke: Another pioneer who used microscopes to observe microorganisms.

Diversity in Microorganisms: Major Groups

Microorganisms are classified into four primary groups, plus a fifth unique category (Viruses).

Bacteria

• Characteristics: Simple, unicellular, and the oldest form of life. They are heterotrophic (most) or autotrophic (some).

• Growth Conditions: They require food, moisture, and warmth.

• Reproduction: Mainly through binary fission, where one parent cell divides into two daughter cells.

• Types by Shape:

  • Coccus (Spherical): e.g., Streptococcus pneumoniae, Staphylococcus aureus.

  • Bacilli (Rod-shaped): e.g., Lactobacillus, E.coli, Salmonella.

  • Spirillum (Spiral-shaped): e.g., Spirillum minus, Helicobacter pylori.

  • Vibrio (Comma-shaped): e.g., Vibrio cholerae, Vibrio vulnificus.

Algae

• Characteristics: Known as "sea weeds" (Latin: Alga). They are autotrophic as they contain chlorophyll for photosynthesis. They show both sexual and asexual reproduction (binary fission, spore formation, fragmentation).

• Size: Range from microscopic unicellular forms to multicellular structures several metres long.

• Examples: Spirogyra (multicellular filamentous), Chlamydomonas (motile via flagella), and Volvox.

Fungi

• Characteristics: Non-green organisms lacking chlorophyll. They can be unicellular (e.g., Yeast) or multicellular (e.g., Bread mould). They are either parasites or saprophytes.

• Growth: Thrive in moist, warm conditions on organic matter like bread, rotting vegetables, leather, and clothes.

• Reproduction: Budding (e.g., Yeast) or spore formation (e.g., Moulds). Fungal spores are light and easily carried by air.

Protozoa

• Characteristics: Derived from "protos" (primitive) and "zoan" (animal). They are primitive animal-like organisms that are aquatic (fresh/sea water) or parasitic.

• Locomotion: Use pseudopodia (Amoeba), cilia (Paramecium), or flagella (Euglena). Sporozoa lack locomotory organs as adults.

• Nutrition: Mostly heterotrophic (holozoic, saprotrophic, parasitic, or symbiotic). Euglena is an exception.

• Reproduction: Binary fission, multiple fission, budding, or spore production.

Viruses

• Characteristics: "Virus" means toxin or poison. They are ultramicroscopic and can only multiply inside living host cells. They are considered a link between living and non-living.

• Shapes: Rod-shaped, cuboidal, spherical, wire-like, or polygonal.

• Bacteriophages: Viruses that specifically infect bacterial cells.

• Lifecycle: Outside the host cell, they are inactive. Inside, they multiply rapidly, eventually bursting the host cell to infect others.

Activity 4.1: Observing Soil Microbes

• Materials: Beaker, soil, water, microscope.

• Procedure: Mix moist soil with water in a beaker. Once settled, observe a drop of the water under a microscope.

• Observation: Tiny organisms are seen moving.

• Conclusion: Soil contains many microscopic living things.

Friendly Microbes

Many microbes are essential for life and human industry.

Environment and Agriculture

• Decomposition: Bacteria, fungi, and protozoa break down organic waste (dead plants/animals), recycling nutrients.

• Bioremediation: Genetically modified Pseudomonas bacteria ("oil-eating bacteria") are used to clean oil spills.

• Nitrogen Fixation: Conversion of atmospheric nitrogen to biologically available forms (e.g., ammonia).

  • Rhizobium lives in root nodules of leguminous plants (pea, soybean).

  • Free-living soil bacteria: Azotobacter, cyanobacteria, and blue-green algae.

• Biofertilisers: Seaweed is used as manure (rich in nitrogen, potassium).

Food Industry

• Curd and Cheese: Lactobacillus converts milk to curd at temperatures between $30\text{ to }40\,^{\circ}\text{C}$ by producing lactic acid.

• Fermentation: The breakdown of sugar by yeast in the absence of oxygen to release $CO_2$. Used in making bread, wine, alcohol, and vinegar.

• Mushrooms: Button and oyster mushrooms are rich in proteins and Vitamin B, low in fat, and cholesterol-free.

• Food Supplements: Algae like Spirulina and Agar (from red algae) are used in ice creams, jellies, and desserts. Brown algae provide iodine and potassium.

Medicines

• Antibiotics: Medicines that kill or stop bacteria. Chloromycetin and Streptomycin come from bacteria. Penicillin comes from the fungus Penicillium.

• Vaccines: Prepared from killed or weakened germs to help the immune system recognize and destroy future infections. Used for Rabies, etc.

• Probiotics: Good bacteria/yeast that improve gut health and immunity.

• Other: Yeast and bacteria are used for Vitamin B production. Genetically modified bacteria are used to produce insulin.

Discovery of Penicillin

• Scientist: Sir Alexander Fleming (1928).

• Discovery: While experimenting with Staphylococcal bacteria, he noticed a contaminated petri dish where a mould (Penicillium notatum) had killed the bacterial colonies. This led to the first antibiotic.

Harmful Microbes (Pathogens)

Human Diseases

• Communicable Diseases: Transmitted via air, water, food, or contact (e.g., Cholera, Tuberculosis, Chicken pox).

• Vectors: Organisms that carry pathogens (e.g., Housefly, Female Anopheles mosquito for Malaria, Female Aedes mosquito for Dengue).

• Specific Human Pathogens:

  • Viruses: Rhinovirus (Common cold), HIV (AIDS), Influenza, Polio, Rabies.

  • Bacteria: Tuberculosis, Typhoid, Cholera.

  • Protozoa: Plasmodium vivax (Malaria), Entamoeba histolytica (Amoebic dysentery), Trypanosoma (African sleeping sickness).

  • Fungi: Athlete's foot, Ringworm.

Animal and Plant Diseases

• Animals: Anthrax (bacteria in cattle), Foot and mouth disease (virus in hooved animals), Rabies (dogs).

• Plants: Bacterial leaf spot, Citrus canker, Crown gall (root/stem), Tobacco mosaic virus (TMV), Blight of potato (fungi), Corn smut (fungi), Rust of wheat (fungi).

Food Spoilage and Preservation

Food Spoilage

• Causes: Microbial growth producing toxins. Indicators include bad odour, slime, discoloration, and gas bubbles/bloated packaging.

• Food Poisoning: Illness from consuming contaminated food. Risk increases during monsoons due to high water contamination and breeding vectors.

Preservation Methods

• Drying (Dehydration): Removes water (sun drying) to prevent microbial growth.

• Refrigeration/Freezing: Low temperatures inactivate enzymes and prevent multiplication.

• Pasteurisation: Milk is heated to $70\,^{\circ}\text{C}$ for $30\text{ minutes}$ and rapidly cooled.

• Salt and Sugar: Draw out water (osmosis). Salt is used for pickles/brine; sugar for jams/jellies.

• Chemical Preservatives: Sodium benzoate and potassium metabisulphite act as antioxidants to remove oxygen.

• Oil and Vinegar: Create a barrier against microbes.

• Canning/Vacuum Packing: Heating to $110\,^{\circ}\text{C}$ and sealing to eliminate air.

• Irradiation: Using high-energy radiation to destroy microorganisms.

Activity 4.2: Fermentation Observation

• Aim: To observe fermentation.

• Procedure: Fill a bottle with sugar solution and yeast powder. Place a deflated balloon over the mouth.

• Observation: The balloon inflates due to $CO_2$ formation.

• Conclusion: Yeast releases carbon dioxide gas during fermentation, which turns lime water milky.

Check Your Progress: Answers/Completion

Part 1

1. Bacteria, fungi, protozoa and Algae are the four major groups of microorganisms.

2. Viruses are considered different because they multiply only inside a host cell.

3. Yeast reproduce by budding.

4. Vibrio are curved-shaped (comma-shaped) bacteria.

Part 2

1. Milk undergoes Pasteurisation to become germ-free.

2. Food Poisoning is a term for health problems from contaminated food.

3. The female Aedes mosquito acts as a carrier of dengue virus.

4. Diseases transmitted between persons are communicable diseases.