Chapter 7: Introduction to Microbiology

The fascinating world of microorganisms - studying microscopic life forms that impact our health, environment, food, and industries.

Bacteria
Fungi
Viruses
Protozoa
Algae
Microbes

1. Introduction

Microbiology is the branch of science that deals with the study of microorganisms, which are living organisms too small to be seen with the naked eye. These organisms can be observed using microscopes. Microorganisms are found everywhere – in air, water, soil, and even inside living bodies.

2. Microorganisms

Microorganisms are also called microbes. They include both useful and harmful organisms that play crucial roles in various biological processes.

Common Features of Microorganisms:

  • Microscopic in size (require microscope to be seen)
  • Can survive in extreme environments (hot springs, deep sea, ice)
  • Some are unicellular, others multicellular
  • Rapid reproduction rate
  • High metabolic activity
  • Ubiquitous distribution (found everywhere)

3. Types of Microorganisms

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3.1 Bacteria

Bacteria are unicellular prokaryotic organisms found in almost all environments on Earth.

Characteristics:

  • Unicellular prokaryotes (no nucleus)
  • Size: 0.5-5 micrometers
  • Shapes: Cocci (spherical), Bacilli (rod-shaped), Spirilla (spiral)
  • Cell wall contains peptidoglycan
  • Can be autotrophic or heterotrophic
  • Reproduce by binary fission

Uses of Bacteria:

  • Making curd, cheese, yogurt (Lactobacillus)
  • Nitrogen fixation in soil (Rhizobium)
  • Production of antibiotics (Streptomyces)
  • Sewage treatment
  • Vitamin production in human gut
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3.2 Fungi

Fungi are eukaryotic organisms that include mushrooms, molds, and yeasts.

Characteristics:

  • Mostly multicellular (except yeasts)
  • Cell wall made of chitin
  • Heterotrophic (saprophytic or parasitic)
  • Grow on decaying organic matter
  • Reproduce by spores

Uses of Fungi:

  • Production of bread (yeast fermentation)
  • Alcohol production (brewing, winemaking)
  • Antibiotic production (Penicillium → Penicillin)
  • Food source (mushrooms)
  • Decomposition of organic matter

Examples:

  • Yeast (Saccharomyces cerevisiae)
  • Mushroom (Agaricus)
  • Penicillium (antibiotic producer)
  • Aspergillus (food spoilage)
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3.3 Protozoa

Protozoa are unicellular eukaryotic microorganisms, mostly found in aquatic environments.

Characteristics:

  • Unicellular and microscopic
  • Eukaryotic (have nucleus and organelles)
  • Mostly found in water bodies
  • Heterotrophic (feed on bacteria, organic matter)
  • Motile (move using cilia, flagella, or pseudopodia)

Examples:

  • Amoeba (moves using pseudopodia)
  • Paramecium (moves using cilia)
  • Plasmodium (causes malaria)
  • Entamoeba (causes amoebic dysentery)
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3.4 Algae

Algae are photosynthetic microorganisms that can be unicellular or multicellular.

Characteristics:

  • Photosynthetic (contain chlorophyll)
  • Mostly aquatic (freshwater and marine)
  • Can be unicellular or multicellular
  • Cell wall made of cellulose
  • Autotrophic (produce own food)

Importance of Algae:

  • Produce about 50% of Earth's oxygen
  • Form the base of aquatic food chains
  • Used as food (seaweed, spirulina)
  • Source of agar and alginates (food industry)
  • Biofuel production potential
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3.5 Viruses

Viruses are unique microorganisms that exist at the borderline of living and non-living.

Characteristics:

  • Non-cellular structure (acellular)
  • Obligate intracellular parasites
  • Reproduce only inside host cells
  • Consist of genetic material (DNA or RNA) surrounded by protein coat
  • Extremely small (20-400 nm)

Examples of Viral Diseases:

  • Influenza (Flu virus)
  • Measles (Measles virus)
  • COVID-19 (SARS-CoV-2)
  • Polio (Poliovirus)
  • HIV/AIDS (Human Immunodeficiency Virus)
Microorganism Cell Type Size Range Nutrition Examples
Bacteria Prokaryotic 0.5-5 μm Autotrophic/Heterotrophic E. coli, Lactobacillus
Fungi Eukaryotic 2-10 μm (yeast), larger (molds) Heterotrophic Yeast, Mushroom, Penicillium
Protozoa Eukaryotic 10-50 μm Heterotrophic Amoeba, Paramecium
Algae Eukaryotic 1 μm - several meters Autotrophic Spirogyra, Chlamydomonas
Viruses Acellular 20-400 nm Parasitic Influenza, HIV, COVID-19

4. Useful Microorganisms

Microorganisms play beneficial roles in various fields and are essential for life on Earth.

4.1 Food Industry

  • Making curd, yogurt, cheese (Lactobacillus bacteria)
  • Bread making (yeast fermentation)
  • Alcohol production (brewing, winemaking)
  • Vinegar production (Acetobacter)
  • Pickle and sauerkraut fermentation

4.2 Medicine

  • Antibiotic production (Penicillin from Penicillium)
  • Vaccine development (weakened/killed microbes)
  • Insulin production using genetically modified bacteria
  • Vitamin production (Vitamin B12, K by gut bacteria)
  • Probiotics for digestive health

4.3 Agriculture

  • Nitrogen fixation (Rhizobium in legume roots)
  • Biofertilizers (Azotobacter, Azospirillum)
  • Biocontrol agents (Bacillus thuringiensis as pesticide)
  • Composting and organic matter decomposition
  • Mycorrhizal fungi enhancing nutrient uptake

4.4 Environment

  • Decomposition of organic waste (biodegradation)
  • Recycling nutrients in ecosystems
  • Sewage treatment (aerobic and anaerobic bacteria)
  • Bioremediation (cleaning oil spills, toxic waste)
  • Carbon cycling and oxygen production

5. Harmful Microorganisms

Some microorganisms cause diseases (pathogens) in humans, animals, and plants.

Diseases in Humans Caused by Microbes:

Disease Causing Microbe Type of Microbe Transmission
Cholera Vibrio cholerae Bacteria Contaminated water/food
Tuberculosis Mycobacterium tuberculosis Bacteria Airborne droplets
Malaria Plasmodium vivax/falciparum Protozoa Mosquito bite
COVID-19 SARS-CoV-2 Virus Airborne, contact
Typhoid Salmonella typhi Bacteria Contaminated food/water
Dengue Dengue virus Virus Mosquito bite

Diseases in Plants Caused by Microbes:

  • Citrus canker - Bacterial disease affecting citrus plants
  • Rust of wheat - Fungal disease causing reddish-brown spots
  • Blast of rice - Fungal disease affecting rice crops
  • Tobacco mosaic virus - Viral disease in tobacco plants
  • Powdery mildew - Fungal disease in various plants

6. Prevention and Control of Microbial Diseases

Methods to Prevent Microbial Diseases:

  • Vaccination - Immunization against specific diseases
  • Maintaining personal hygiene - Regular hand washing, cleanliness
  • Safe drinking water - Boiling, filtration, chlorination
  • Proper sanitation - Waste disposal, sewage treatment
  • Food safety - Proper cooking, refrigeration, avoiding contamination
  • Vector control - Mosquito nets, insect repellents
  • Antibiotics - For bacterial infections (prescribed by doctors)
  • Isolation and quarantine - For contagious diseases

7. Industrial Applications of Microorganisms

Major Industrial Uses:

  • Antibiotic production - Penicillin, streptomycin, tetracycline
  • Enzyme production - Amylase, protease, lipase for detergents, food processing
  • Alcohol production - Ethanol for beverages, fuel, solvents
  • Organic acid production - Citric acid, acetic acid, lactic acid
  • Waste treatment - Biodegradation of industrial effluents
  • Biogas production - Methane from organic waste
  • Biotechnology - Genetic engineering, recombinant DNA technology
  • Single-cell protein - Nutritional supplements from microbes

8. Role of Microorganisms in Environment

  • Decomposition - Breaking down dead organisms and organic waste
  • Nutrient cycling - Carbon, nitrogen, phosphorus, sulfur cycles
  • Sewage treatment - Breaking down organic matter in wastewater
  • Bioremediation - Cleaning pollutants from soil and water
  • Symbiotic relationships - Nitrogen fixation, mycorrhizal associations
  • Oxygen production - Photosynthetic algae and cyanobacteria
  • Soil formation - Weathering rocks, organic matter decomposition

9. Importance of Microbiology

  • Helps in medical diagnosis and treatment of diseases
  • Improves agricultural productivity through biofertilizers and biopesticides
  • Supports food and beverage industries
  • Maintains ecological balance through nutrient cycling
  • Advances biotechnology and genetic engineering
  • Contributes to environmental protection and waste management
  • Enhances understanding of life processes at cellular level
  • Develops new vaccines and antibiotics

10. Key Exam Points

Microbiology
Microorganisms
Bacteria
Fungi
Viruses
Protozoa
Algae
Antibiotics
Vaccines
Fermentation
Pathogens
Decomposition
Nitrogen Fixation
Biotechnology
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