Microbiology Lectures 4, 5, and 6 Notes

Overview of Microbiology Lectures 4, 5, and 6

• Module: Biology of the Microbial Cell
• Dates: January 13, 15, and 17, 2025

Electron Microscopy (EM)

• **Advantages: **
  • Higher resolving power than light microscopy
• Types of EM:
  • Transmission Electron Microscopy (TEM):
  • High resolution and magnification
  • Samples must be dead, freeze/dehydrated, and thinly sliced
  • Visualizes sub-cellular and molecular structures
  • Scanning Electron Microscopy (SEM):
  • Electrons bounce off samples, providing a 3D-like appearance
  • Provides images of surfaces

Comparison of Microscopy Techniques

• TEM vs Light Microscopy:
  • TEM Components:
  • Electron gun, electromagnet, objective lens, etc.
  • Light Microscope Components:
  • Light source, objective lens, ocular lens, etc.

Understanding Size and Scale in Microbiology

• Relative Sizes of Organisms (Logarithmic Scale):
  • Variable sizes from 0.1 nm (atoms) to several meters (mycelia)
• Key examples:
  • Viruses: 0.05 - 0.1 μm
  • Bacteria: 1 - 10 μm
  • Eukaryotic cells: 10 - 100 μm

Historical Theories in Microbiology

• Spontaneous Generation Theory:
  • Life arises from nonliving matter.
  • Francesco Redi's Experiments:
  • Provided evidence against this theory.
• Louis Pasteur's Contributions:
  • Proposed life comes only from life, conducted experiments with swan-neck flasks.

Cell Theory

• Key Concepts of Cell Theory:
  • All living organisms are composed of one or more cells.
  • Cells are the basic unit of life.
  • Cells arise from pre-existing cells.
  • Cellular activities determine the overall activities of organisms.
  • Energy flow occurs within cells, containing DNA and RNA.

Endosymbiotic Theory

• Proposed by: Konstantin Mereschkowski, revived by Lynn Margulis.
• Key Processes:
  1. Infolding of the plasma membrane led to endomembrane system creation (nucleus, ER).
  2. Ancestral eukaryote consumed aerobic bacteria → Mitochondria.
  3. Consumed photosynthetic bacteria → Chloroplasts.

Prokaryotic Cells

• Characteristics:
  • Include Bacteria and Archaea.
  • Lack a nucleus; genetic material is located in the cytoplasm.
• Shapes:
  • Coccus (round), Bacillus (rod), Vibrio (curved rod), Spirillum (spiral), Spirochete (long, helical).

Size Variation Among Bacteria

• Size ranges from Mycoplasma (0.1 - 0.5 μm) to Thiomargarita magnifica which is macroscopic.

Prokaryotic Inclusions and Structures

• Functions of Inclusions:
  • Energy storage, gas vesicles, magnetosomes for orientation.
• Endospores:
  • Characteristics:
  • Resistant to extreme temperatures and radiation.
  • Dormant with no metabolic activity.
  • Distinct developmental process leading to spore formation.

Eukaryotic Cells

• Characteristics:
  • Membrane-enclosed nucleus and organelles (e.g., mitochondria, ER).
• Variability in shapes and sizes.

Cell Envelope Components

• Defines the cell structure:
  • Cytoplasmic membrane, cell wall, outer membrane, capsule, S-layer.
• Functionality:
  • Barrier, selective permeability, communication, and protection.

Transport Mechanisms Across Membranes

• Passive Transport:
  • Simple diffusion (no energy), facilitated diffusion (protein-mediated).
• Active Transport:
  • Requires energy to move substances against a concentration gradient (ATP driven).

The Bacterial Cell Wall

• Function: Maintains shape and prevents osmotic lysis.
• Peptidoglycan:
  • Unique to bacteria, structural component that differentiates Gram-positive and Gram-negative bacteria.

Distinguishing Gram-positive and Gram-negative Bacteria

• Gram-positive: Thick peptidoglycan layer, teichoic acids.
• Gram-negative: Thin peptidoglycan, outer membrane containing lipopolysaccharides (LPS).

Bacterial Surface Structures

• Capsules and Slime Layers:
  • Protective polysaccharide layers aiding adhesion and biofilm formation.
• Pili and Flagella:
  • Involved in attachment, movement (twitching, swimming), and conjugation.

Taxis and Movement Mechanisms

• Types of Taxis:
  • Chemotaxis, osmotaxis, hydrotaxis, phototaxis, aerotaxis.
• Motility:
  • Swimming using flagella, with distinct structural differences in Gram-positive and Gram-negative contexts.

Conclusion

• Next Focus: Microbial metabolism and laboratory growth of bacteria. Read Chapters 8 and 9 for preparation.