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.