Main Themes of Microbiology

Introduction to Microbiology

Microbiology is the scientific study of living organisms that are too small to be seen with the unaided eye. These organisms, known as microorganisms or microbes, play essential roles in the environment, human health, and industry.

• Micro-: Refers to things so small they cannot be seen by the naked eye.

• -biology: The study of living things.

Microbiology encompasses the study of various types of microorganisms, including bacteria, fungi, protozoa, viruses, algae, and archaea.

How Small is Small? Measuring Microbes

Scale of Microorganisms

Microorganisms are measured using the metric system, often in units much smaller than those used in everyday life.

• Micrometer (μm): 1 μm = meters

• Nanometer (nm): 1 nm = meters

• Angstrom (Å): 1 Å = 0.1 nm = meters

Examples of sizes:

• Red blood cell: ~10 μm

• Amoeba: ~100 μm

• HIV virus: ~100 nm

• DNA diameter: ~2 nm

Types of Microorganisms

Major Groups of Microbes

Microorganisms are classified into several major groups based on their cellular structure and function:

• Bacteria (prokaryotes): Unicellular, lack a nucleus, found in diverse environments. Example: Escherichia coli.

• Fungi (eukaryotes): Can be unicellular (yeasts) or multicellular (molds, mushrooms). Example: Cladosporium (mold).

• Protozoa (eukaryotes): Unicellular, heterotrophic, often found in moist environments. Example: Paramecium.

• Viruses (acellular): Not composed of cells, consist of genetic material (DNA or RNA) surrounded by a protein coat (capsid), sometimes with an envelope. Require a host cell to reproduce.

• Algae (eukaryotes): Photosynthetic, can be unicellular or multicellular.

• Archaea (prokaryotes): Similar to bacteria but with distinct genetic and biochemical characteristics, often found in extreme environments.

Cellular Organization: Prokaryotes vs. Eukaryotes

Microorganisms can be classified based on their cellular structure:

Viruses: Unique Microbes

• Acellular, not made of cells.

• Obligate intracellular parasites—can only reproduce inside a host cell.

• Structure: Genetic material (DNA or RNA), protein coat (capsid), sometimes an envelope with spikes.

• Some viruses can survive outside a host for varying periods (e.g., HIV dies quickly, flu virus survives up to 48 hours).

Microbial Communities

• Microorganisms often live in groups, forming visible colonies or biofilms.

• Biofilms: Communities of microbes attached to surfaces (e.g., riverbeds, medical devices).

• Bacterial colonies: Groups of bacteria growing together, often secreting substances to adhere to each other and surfaces.

Importance and Applications of Microbes

Positive Roles of Microorganisms

• Food production: Cheese, bread, beer.

• Antibiotic production.

• Medical research and genetic engineering.

• Essential in nutrient cycling (e.g., in soil, oceans).

• Water purification and bioremediation (e.g., cleaning oil spills).

Note: Only about 1% of microbes cause disease; most are beneficial or harmless.

Scientific Notation and Metric Measurement

Scientific Notation

Scientific notation is used to express very large or very small numbers conveniently.

• Format: Single digit value (between 1 and 10) × power of ten.

• Example: 0.00000000054 =

• To convert: Move the decimal so the number is between 1 and 10, count the moves for the exponent.

• Moving left: positive exponent; moving right: negative exponent.

Exponent rules:

• Multiplying: Add exponents ()

• Dividing: Subtract exponents ()

Metric System Units

History of Microbiology

Early Discoveries

• Robert Hooke (1635–1703): First to see and describe cells; coined the term "cell" after observing cork under a microscope.

• Antonie van Leeuwenhoek (1632–1723): First to observe bacteria and protozoa ("animalcules") using handcrafted microscopes with up to 500x magnification.

Spontaneous Generation vs. Biogenesis

• Spontaneous generation (abiogenesis): The outdated belief that living things could arise from non-living matter (e.g., maggots from meat).

• Francesco Redi (1626–1697): Disproved spontaneous generation for larger organisms using controlled experiments with meat and jars.

• Lazzaro Spallanzani (1729–1799): Showed that sealed and boiled broth did not produce microbial growth, challenging spontaneous generation for microbes.

• Louis Pasteur (1822–1895): Definitively disproved spontaneous generation with swan-neck flask experiments; established the principle of biogenesis (life comes from life).

Contributions to Microbiology

• Louis Pasteur: Demonstrated the role of microbes in fermentation and spoilage; developed pasteurization; contributed to the germ theory of disease.

• Hidden Figures:

  • Ella Moore: First African American woman to earn a PhD in natural science; contributed to tuberculosis research.

  • Fanny Hesse: Introduced agar as a solidifying agent for culture media.

  • Ruth Ella Moore, Annie Alexander, and others: Made significant contributions to vaccines, malaria research, and antibiotic resistance.

Recent Discoveries and Challenges

• Development of the electron microscope (enabled visualization of viruses and cell structures).

• Discovery of antibiotics and vaccines.

• Emergence of antibiotic resistance as a major public health challenge.

Summary Table: Key Historical Figures

Additional info: Some details about hidden figures and their contributions were inferred and expanded for academic completeness.