Bacteria & Archaea

Overview of the Lecture

• Subject: Microbiology focusing on Bacteria and Archaea

• Lecturer: Dr. Steve Bauer, Ph.D.

• Course Codes: BIO 202-105, 106, & 107

• Date: January 27, 2026

• Visuals: Includes images and diagrams relevant to Microbiology

Table of Contents

1. Bacterial Cell Structure

2. Bacterial Cell Shapes & Arrangements

3. Bacterial Structures Involved In Movement & Attachment

4. Bacterial Cell Wall & Plasma Membrane

5. Gram Character of Bacteria (Gram + or Gram -)

6. Bacterial Genetic Material & Contents

7. Archaea Are "Extremophiles"

8. Classification Systems For Bacteria & Archaea

Bacteria & Archaea: An Overview

• Comparison with Eukaryotes:

  • Differences include:

    • Packaging of DNA: Bacteria and Archaea lack a nucleus (they are prokaryotes).

    • Composition of cell wall: Bacteria have peptidoglycan, while Archaea have pseudomurein.

    • Internal structures: Both lack membrane-bound organelles.

Bacterial Cell Structure

• Essentials of Bacterial Cells:

  • All bacteria possess:

    • Cell membrane (plasma membrane)

    • Cytoplasm

    • Ribosomes

    • A singular, circular chromosome

  • Many bacteria also have:

    • Glycocalyx: A type of polysaccharide coating.

Some Bacterial Cells Also Possess

• Additional Features:

  • Flagella, pili, and fimbriae: Involved in movement and attachment.

  • Outer membrane (capsule): Outside the plasma membrane.

  • Plasmids: Extrachromosomal DNA.

  • Endospores: Protect against harsh environmental conditions.

Bacterial Cell Shapes

• Life Forms: Most bacteria are unicellular organisms.

• Shapes: There are three main shapes of bacteria:

  • Coccus: Round

  • Bacillus: Rod-shaped

  • Spirals: Includes spirillium, spirochete, and vibrio.

• Examples:

  • Coccus: Staphylococcus aureus

  • Bacillus: Bacillus anthracis

  • Spiral: Treponema pallidum

Bacterial Arrangements: Cocci

• Variability in Arrangement:

  • Single: Circular

  • Diplococci: Pairs of cells

  • Tetrads: Groups of four cells

  • Staphylococci: Grape-like clusters

  • Streptococci: Chains of cells

• Scientific Naming:

  • Uses a binomial system:

    • Latin-based.

    • First name is capitalized and italicized; second name is lowercase and italicized.

Bacterial Arrangements: Bacilli

• Basic Structures:

  • Single Rod: One cell

  • Diplobacilli: A pair of cells attached at ends

  • Streptobacilli: Chains of cells

External Structures of Bacteria Involved in Mobility

• Flagella: Tail-like structures that provide motility to bacteria.

• Axial Filaments: Spirochete structure for unique movement.

Arrangement of Bacterial Flagella

• Types of Flagella Arrangements:

  • Monotrichous: Single flagellum

  • Lophotrichous: Bunches of flagella at one end

  • Amphitrichous: Flagella at each pole of the cell

  • Peritrichous: Flagella spread over the surface

Chemotaxis & Flagella Function

• Definition: Movement in response to chemical signals.

  • Positive Chemotaxis: Movement toward a favorable chemical stimulus (e.g., nutrients).

  • Negative Chemotaxis: Movement away from a chemical stimulus.

Fimbriae

• Description: Small, bristle-like fibers for adhesion to host tissues, aiding in colonization and infection.

Pilus/Pili

• Function: Used for genetic material exchange during conjugation.

  • Mnemonic: “Conjugal Visits” - a reminder of their role in connection between bacterial cells.

Glycocalyx

• Composition: A polysaccharide outer coating.

  • Slime Layer: Loose structure, aids in protection against water and nutrient loss.

  • Capsule: Tightly bound, denser, and acts as a protective barrier.

Capsules & Biofilms

• Capsules: Enhance the pathogenicity of bacteria.

• Biofilms: Complex communities that enable persistent colonization of surfaces such as teeth and medical devices.

Plasma Membrane & Cell Wall Structure

• Composition: Encloses the content; plasma membrane is internal to the cell wall.

• Plasma Membrane: Phospholipid bilayer with proteins. Some proteins create channels, while others are glycoproteins and glycolipids.

• Fluid Mosaic Model: Describes the membrane's structure and function, where proteins float in a phospholipid layer.

Plasma Membrane Function

• Selective Permeability: Allows certain molecules to pass, crucial for maintaining cellular homeostasis.

The Cell Wall

• Role: Determines bacterial shape and provides structural support against osmotic pressure.

• Gram Staining: Differentiates between Gram-positive and Gram-negative bacteria based on cell wall composition:

  • Gram-Positive: Thick peptidoglycan layer.

  • Gram-Negative: Thin peptidoglycan layer plus an outer membrane.

Peptidoglycan

• Definition: A polysaccharide framework that provides structural support.

• Antibiotic Target: Many antibiotics disrupt peptidoglycan synthesis to kill bacteria.

Gram-Positive & Gram-Negative Cell Walls

• Gram-Positive Structure:

  • Thick peptidoglycan and teichoic acids link cell walls to plasma membrane.

• Gram-Negative Structure:

  • Thin peptidoglycan and outer membrane of lipopolysaccharides (LPS), acts as an additional barrier.

Atypical Cell Walls

• Acid-Fast Cell Walls:

  • Similar to Gram-positive but contain waxy lipids (mycolic acid).

• Examples: Mycobacterium species, including Mycobacterium tuberculosis.

Archaea

• Characteristics: Unique membranes and distinct cell walls lacking peptidoglycan.

  • Use pseudomurein in their cell walls.

  • Many are extremophiles living in harsh environments but also found in normal, less extreme ecosystems.

Comparison of 3 Domains of Life

Classification Systems For Bacteria & Archaea

• Bergey's Manuals:

  • Systematic: Comprehensive view based on genetic screening.

  • Determinative: Based on phenotypic characteristics useful in lab settings, focusing on observable traits.

Useful Review Resources

• Links to YouTube videos and practice questions relevant to the content discussed in lecture.