MICR20010 - lecture 4 2023.pptx

MICR20010 Lecture 4 Basic microbial morphology Dr. Jennifer Mitchell Microbiology School of Biomolecular and Biomedical Science Lecture 3 • • • • • • • • Light Microscopy Preparing bacterial cells for microscopy Light microscope resolution Electron Microscope – Scanning Electron Microscope – Tra...

MICR20010 Lecture 4 Basic microbial morphology Dr. Jennifer Mitchell Microbiology School of Biomolecular and Biomedical Science Lecture 3 • • • • • • • • Light Microscopy Preparing bacterial cells for microscopy Light microscope resolution Electron Microscope – Scanning Electron Microscope – Transmission Electron Microscope Domains of Life Types of microorganism Eukaryotic Cell Structure Eukaryotic Versus Prokaryotic Cells Learning Outcomes • Prokaryotic cell morphology • Bacterial cell structure • The gram stain – Gram stain mechanism • Bacterial shapes – Different morphological shapes • Bacterial cell structure – G+ve G-ve Archaea – – – – Cell membrane Cell wall Outer membrane Cell appendages Prokaryotic cells Bacteria Gram positive Gram negative Archaea Bacterial Cell Structure The Gram Stain Most important differential staining method in Microbiology Gram-positive (staphylococci) Gram-negative (Escherichia coli) 1. Crystal Violet 2. Iodine 3. Alcohol 4. Neutral Red Gram Stain Mechanism • Differential lipid content of G+ and G- cell envelopes • Crystal violet-iodine complex forms within the cells (Blue colour) • Alcohol treatment G- cell envelope has high lipid content which is extracted by alcohol to permeabilise the membrane G+ cell envelope has low lipid content and is dehydrated by alcohol - making it impermeable Crystal violet-iodine complex diffuses out and neutral red is taken up Some bacteria don’t stain using the Gram method Mycobacteria have a high wax content in their cell envelope and suspected mycobacteria are stained using the ZiehlNielson stain Mycoplasmas, the smallest known bacteria, have no cell wall to stain Bacterial Shapes • Cocci (spherical) • Bacilli (rod shaped) • Curved or spiral shaped Morphological Shapes of Different Bacteria Thiomargarita magnifica Bacterial Cell Structure • Chromosome The bacterial chromosome contains the bacterial genetic information. Plasmids may also be present. • Cytoplasmic Membrane The cytoplasmic membrane surrounds the cytoplasm • Cell Wall Rigid layer surrounding the cytoplasmic membrane • Outer Membrane of Gram-negative bacteria Covers the cell wall and acts as a molecular sieve Typical Gram-negative and Gram-positive Cell Envelopes Cytoplasmic Membrane • Composed primarily of lipids and phospholipids • Osmotic barrier – Only molecules smaller than glycerol diffuse into the cytoplasm • Site of energy production oxidative phosphorylation • Transport of important molecules via Permeases • Facilitated diffusion (passive) and Active transport • Synthesis of new cell wall • Anchor the chromosome Cell Wall Domains of Life 1. Eukaryotes Cell wall composed primarily of peptidoglycan 2. Bacteria 3. Archaea Prokaryotes Lack peptidoglycan - wall composed of other polysaccharides or proteins Function of the cell wall Bacterial cells contain high concentrations of dissolved solutes (salts, sugars etc). Generates a high pressure within the cell caused by the cytoplasm pressing against the cell envelope (similar to pressure in car tyre) Cell wall allows cell to withstand turgor pressure Gives the cell shape and rigidity Bacterial Cell Wall Peptidoglycan = the principal component of the cell wall, is a unique polysaccharide which gives the cell its characteristic shape and prevents osmotic lysis Gram-positive Many peptidoglycan layers (90% of cell envelope material) Gram-negative One peptidoglycan layer (2-20% of cell envelope material) • Penicillin disrupts peptidoglycan synthesis • Many antigens are presented on cell wall surface Peptidoglycan NAG = N-acetylglucosamine NAM = N-acetylmuramic acid Basic structure of the peptidoglycan disaccharide unit (left) and multiple peptidoglycan units liked to give the cell wall structure (right Amino acids G = N-acetylglucosamine M = N-acetylmuramic acid G-M: b 1,4 glycosidic bond Gram-positive cell envelope Cell walls of Archaea • No peptidoglycan • S-layer composed of a ordered layer of protein or glycoprotein – Examples: Many thermophiles, halophiles, methanogens • Few Archaea contain pseudopeptidoglycan – (Repeated sugar units, however, ab1,3-linked) – Example: Methanogens • Polysaccharides Gram-negative Cell Envelope: Outer Membrane Phospholipid-Lipopolysaccharide (LPS) Bilayer (extra lipid layer - mechanism of the Gram stain) • Bacterial cell adhesion • Resistance to phagocytosis • Molecular sieve - access of some molecules to cell wall and cytoplasmic membrane LPS vs Phospholipid Gram-negative cell envelope Gram positive cell surface Note different surface textures Gram negative cell surface Cell Appendages and other Cell Structures Flagella and Pili extend from the cell surface Flagellae rotate and are required for motility (chemotaxis) Bacteria swim towards chemoattractants and away from chemorepellents Flagella Bacteria use flagella to swim. Changing the direction of the flagellar rotation can cause the cell to tumble and change direction. Pili (from latin for hair) • Common Pili - adherence UTI’s Conjugative Pili - plasmid transfer Further Reading • Microbiology an Introduction, Tortora, Funke and Case 12th Ed. • Chapter 4 “Functional Anatomy of Prokaryotic and Eukaryotic Cells”