BIO153 Lecture 7

Lecture Overview

  • Lecture Title: Anatomy of Bacteria

  • Course: BIO153 Diversity of Organisms

  • Instructor: Ichiro Inamoto

  • Location: University of Toronto Mississauga

Classifying Bacteria

  • Electron Microscopy: Images of four bacterial species utilized for classification.

    • Note: Colors in images are artificial and do not represent actual traits.

  • Classification:

    • Species D, E, H: Gram-positive bacteria.

    • Species C: Gram-negative bacteria, distinct from D, E, H.

  • Specific Bacterial Examples:

    • Salmonella enterica: Gram-negative bacillus.

    • Streptococcus pyogenes: Gram-positive cocci.

    • Listeria monocytogenes: Gram-positive bacillus.

    • Staphylococcus aureus: Gram-positive cocci.

Bacterial Cell Shapes

  • Common Shapes:

    • Coccus (spherical): Can occur as single cells, pairs (diplococcus), or chains (streptococcus), or clusters (staphylococcus).

    • Bacillus (rod-shaped): Can be single (bacillus) or in chains (streptobacillus).

    • Other shapes include vibrio (crescent) and spiral.

Morphological Features of Bacterial Cells

  • Key Structures:

    • Plasma Membrane: Lipid bilayer composed of fatty acids.

    • Capsule/Slime Layer: Provides protection and aids in adherence.

    • Flagella: Tail-like structure used for movement.

    • Pili/Fimbriae: Surface structures for attachment and genetic exchange.

    • Endospores: Survival structures forming under stress.

Plasma Membrane Structure

  • Lipid Bilayer:

    • Composed of hydrophilic heads facing outward and hydrophobic tails inward, creating a barrier.

  • Permeability:

    • Small uncharged molecules (O2, CO2) diffuse easily.

    • Larger or charged molecules (e.g., glucose) do not diffuse freely.

Peptidoglycan Structure

  • Description:

    • Composed of sugars and amino acids, forming a mesh-like structure outside the plasma membrane.

    • Provides mechanical strength to help resist osmotic pressure.

Types of Bacterial Cell Walls

  • Gram Positive:

    • Thick layer of peptidoglycan; simpler structure.

  • Gram Negative:

    • Thin layer of peptidoglycan; has an outer membrane providing additional protection.

Gram Staining Process

  • Procedure: Stains differentiate Gram-positive (purple) and Gram-negative (pink) bacteria.

    1. Stain with crystal violet.

    2. Destain with ethanol.

    3. Stain again with safranin.

  • Clinical Relevance: Rapidly identifies bacterial types for targeted treatment.

Antibiotics and Peptidoglycan

  • Target of Action: Many antibiotics, like penicillin, inhibit peptidoglycan synthesis.

  • Effectiveness: Influenced by whether the bacterial cell wall is Gram-positive or Gram-negative.

Capsules and Slime Layers

  • Structure: Composed of polysaccharides and/or peptides.

  • Function: Provides resistance to desiccation, protection against immune systems, and aids in adhesion.

Sub-Cellular Structures

  • Bacteria possess structured organelles, such as:

    • Thylakoids: Involved in photosynthesis in cyanobacteria.

    • Carboxysomes: Protein structures crucial for CO2 fixation.

Flagella and Mobility

  • Role: Enables movement by rotating; involved in chemotaxis (movement towards favorable conditions).

  • Structural Difference: Varies significantly from eukaryotic flagella, demonstrating convergent evolution.

Fimbriae and Pili

  • Fimbriae: Short, hair-like structures aiding in attachment.

  • Pili: Longer structures facilitating horizontal gene transfer between cells.

Endospores: Survival Mechanism

  • Mechanism: Developed by some Gram-positive bacteria (e.g., Bacillus subtilis) under stress; withstand extreme conditions until environmental conditions improve.

Endospores and Astrobiology

  • Research: NASA experiments exploring the survivability of Bacillus subtilis spores in space conditions to assess potential for contamination of other planets, such as Mars.

Image Credits

  • Various citations for images used throughout the presentation.