Core Concepts in Microbiology: Study Guide for Lectures 2–7

Lecture 2: Foundations of Microbiology

Important Microbiologists and Their Contributions

Microbiology has been shaped by the work of many scientists whose discoveries laid the foundation for the field.

• Louis Pasteur: Disproved spontaneous generation, developed pasteurization, and contributed to vaccine development.

• Robert Koch: Established methods for isolating bacteria and formulated Koch's postulates.

• Other notable figures: Antonie van Leeuwenhoek (first to observe microbes), Joseph Lister (aseptic surgery), Alexander Fleming (discovered penicillin).

Germ Theory

Germ theory states that specific diseases are caused by specific microorganisms. This concept revolutionized medicine and public health.

• Proposed by Louis Pasteur and Robert Koch.

• Led to the development of sterilization, vaccination, and antibiotics.

Koch's Postulates

Koch's postulates are a set of criteria used to establish a causative relationship between a microbe and a disease.

1. The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.

2. The microorganism must be isolated from a diseased organism and grown in pure culture.

3. The cultured microorganism should cause disease when introduced into a healthy organism.

4. The microorganism must be re-isolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Applications: Used to identify causative agents of diseases such as tuberculosis and anthrax.

Microscopy

Microscopy is essential for visualizing microorganisms. Different types of microscopes and stains are used to observe microbial structure and function.

• Types of main problems: (Additional info: Likely refers to resolving power and contrast in microscopy.)

• Types of microscopes:

  • Light microscope: Used for viewing stained or live cells.

  • Electron microscope: Provides higher resolution for viewing ultrastructure.

• Types of stains:

  • Simple stains: Use a single dye to color cells.

  • Differential stains: (e.g., Gram stain) distinguish between different types of bacteria.

  • Special stains: Highlight specific structures (e.g., endospore stain).

Lectures 3–6: Cell Structure, Classification, and Diversity

Prokaryotes vs. Eukaryotes

Microbial cells are classified as either prokaryotic or eukaryotic based on their structural features.

Feature	Prokaryotes	Eukaryotes
Nucleus	No	Yes
Membrane-bound organelles	No	Yes
Cell wall composition	Peptidoglycan (Bacteria)	Cellulose (plants), chitin (fungi), or none
Size	Smaller (0.5–5 μm)	Larger (10–100 μm)

Timeline of Microbial Life

Microbial life has existed for billions of years, with prokaryotes appearing first, followed by eukaryotes.

• First prokaryotes: ~3.5 billion years ago

• First eukaryotes: ~2 billion years ago

• Development of multicellularity and complex life followed

Macromolecules in Cells

Cells are composed of four major types of macromolecules, each with specific functions.

Macromolecule	Function	Types
Proteins	Enzymes, structure, transport	Enzymes, structural proteins
Nucleic acids	Genetic information storage and transfer	DNA, RNA
Carbohydrates	Energy storage, structure	Monosaccharides, polysaccharides
Lipids	Membranes, energy storage	Phospholipids, triglycerides

Phylogeny vs. Taxonomy

Phylogeny is the evolutionary history and relationships among organisms, while taxonomy is the classification and naming of organisms.

• Phylogeny is often depicted as a tree based on genetic data.

• Taxonomy uses hierarchical ranks: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.

Gram Stain

The Gram stain is a differential staining technique that distinguishes bacteria based on cell wall structure.

• Gram-positive: Thick peptidoglycan layer, stains purple.

• Gram-negative: Thin peptidoglycan layer, outer membrane, stains pink/red.

Major components: Peptidoglycan, teichoic acids (Gram+), lipopolysaccharide (Gram-).

Fluid Mosaic Model

The fluid mosaic model describes the structure of cell membranes as a dynamic arrangement of phospholipids and proteins.

• Membranes are fluid, allowing lateral movement of components.

• Integral and peripheral proteins serve various functions (transport, signaling).

Bacterial Cell Structure

Bacterial cells contain various structures essential for survival and function.

• Cell wall: Provides shape and protection.

• Plasma membrane: Selective barrier for transport.

• Ribosomes: Protein synthesis.

• Nucleoid: Region containing DNA.

• Flagella: Motility.

• Pili/fimbriae: Attachment and conjugation.

• Capsule: Protection from desiccation and immune response.

Endospores

Endospores are highly resistant, dormant structures formed by some bacteria (e.g., Bacillus, Clostridium) to survive harsh conditions.

• Formed in response to nutrient limitation.

• Resistant to heat, desiccation, chemicals, and radiation.

• Identified by special stains and microscopy.

Cell Shapes and Arrangements

Bacteria exhibit a variety of shapes and arrangements, which aid in identification.

• Coccus: Spherical

• Bacillus: Rod-shaped

• Spirillum: Spiral-shaped

• Arrangements: Chains (strepto-), clusters (staphylo-), pairs (diplo-)

Extremophiles

Extremophiles are organisms that thrive in extreme environments.

• Thermophiles: High temperature

• Halophiles: High salt

• Acidophiles: Low pH

• Alkaliphiles: High pH

Domains of Life: Bacteria, Archaea, Eukarya

Life is classified into three domains based on genetic and biochemical differences.

• Bacteria: Prokaryotic, peptidoglycan cell walls.

• Archaea: Prokaryotic, unique membrane lipids, often extremophiles.

• Eukarya: Eukaryotic, includes protists, fungi, plants, animals.

Viruses

Viruses are acellular infectious agents composed of nucleic acid (DNA or RNA) and a protein coat (capsid).

• Obligate intracellular parasites.

• Some have an envelope derived from host membranes.

• Structure varies: helical, icosahedral, complex.

Bacteriophages

Bacteriophages are viruses that infect bacteria. They have diverse life cycles (lytic, lysogenic) and play roles in gene transfer and bacterial ecology.

• Lytic cycle: Virus replicates and lyses host cell.

• Lysogenic cycle: Viral genome integrates into host DNA.

Lecture 7: Culturing Bacteria and Microbial Nutrition

Culturing Microbes

Microbes are grown in the laboratory using various types of media.

Type of Media	Description
Solid/liquid/semi-solid	Physical state of the medium
Defined (synthetic)	Exact chemical composition known
Complex	Contains extracts, composition not fully known
Differential	Distinguishes microbes based on metabolic traits
Selective	Suppresses growth of some microbes, favors others

Culturable vs. Unculturable Microbes

Not all microbes can be grown in the laboratory. Culturable microbes can be isolated and grown on artificial media, while unculturable microbes cannot.

• Unculturable microbes are studied using molecular techniques (e.g., metagenomics).

Trophic Categories and Nutritional Types

Microorganisms are classified based on their energy and carbon sources.

Category	Energy Source	Carbon Source	Example
Photoautotroph	Light	CO2	Cyanobacteria
Chemoautotroph	Inorganic chemicals	CO2	Nitrifying bacteria
Photoheterotroph	Light	Organic compounds	Some purple non-sulfur bacteria
Chemoheterotroph	Organic compounds	Organic compounds	Most bacteria, fungi, animals

Example: A cyanobacterium that performs photosynthesis is a photoautotroph.

Additional info: Some explanations and tables were expanded for clarity and completeness based on standard microbiology curricula.