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IV. Bacterial Structure and Growth

IV. Bacterial Structure and Growth. A. Bacterial Cells: An Overview B. Bacterial Cell Structures C. Factors that Influence Bacterial Growth. IV. A. Bacterial Cells: An Overview. Shapes & Arrangements Round Bacteria Coccus Staphylococcus Diplococcus Tetrad Streptococcus Sarcina

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IV. Bacterial Structure and Growth

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  1. IV. Bacterial Structure and Growth A. Bacterial Cells: An Overview B. Bacterial Cell Structures C. Factors that Influence Bacterial Growth

  2. IV. A. Bacterial Cells: An Overview • Shapes & Arrangements • Round Bacteria Coccus Staphylococcus Diplococcus Tetrad Streptococcus Sarcina • Rod-shaped Bacteria Bacillus Streptobacillus Diplobacillus Coryneform bacteria

  3. IV. A. Bacterial Cells: An Overview • Shapes & Arrangements (cont.) • Curved & Spiral Bacteria Vibrio Spirillum Spirochaete

  4. IV. A. Bacterial Cells: An Overview • Sizes • Typically ~ 0.1 - 20 m (with some exceptions) • Typical coccus: ~ 1 m (eg Staphylococcus) • Typical short rod: ~ 1 x 5 m (eg E. coli) • Barely within the best resolution of a good compound light microscope

  5. IV. A. Bacterial Cells: An Overview

  6. IV. B. Bacterial Cell Structures 1.     Capsules 2.     Cell Wall 3.     Plasma Membrane 4.     Cytoplasm & Cytoplasmic Inclusions 5.     Ribosomes 6.     Bacterial DNA 7.     Pili 8.     Flagella 9.     Spores

  7. IV. B. 1.     Capsules • Species and strain specific • Structure • Polysaccharide or polypeptide layer outside cell wall • May be tightly or loosely bound • Detected by negative staining techniques

  8. IV. B. 1.     Capsules (cont.) • Functions • Attachment • Resistance to desiccation • Nutrient Storage • Evasion of phagocytosis eg. in Streptococcus pneumoniae S strain is encapsulated & virulent R strain is nonencapsulated & nonvirulent

  9. IV. B. 2.     Cell Wall • Gram Staining • Method developed by Gram in 1888 • Gram-positive cells stain purpleGram-negative cells stain pink • Later, it was discovered that the major factor determining Gram reactions is the bacterial cell wall structure • “Gram-positive” & “Gram-negative” These terms can mean either: Staining results, or Types of cell wall structure

  10. IV. B. 2.     Cell Wall • Peptidoglycan Structure • Composition • A Polysaccharide • Composed of alternating units ofN-acetylglucosamine (NAG) andN-acetylmuramic acid (NAM) • Peptide Crosslinking BetweenNAM units • Much thicker and more crosslinking in Gram-positive than in Gram-negative Bacteria

  11. IV. B. 2.     Cell Wall • Gram-positive Cell Wall • Thick Layer of Highly Crosslinked Peptidoglycan • Teichoic Acid Strands

  12. IV. B. 2.     Cell Wall • Gram-negative Cell Walls • Outer Membrane • Lipopolysaccharide Layercontaining Lipid A • Phospholipid Layer • Outer Membrane Proteins • Thin Layer of Peptidoglycanwith no teichoic acid • Periplasmic Space

  13. IV. B. 2.     Cell Wall • Variations on Cell Wall Architecture • Acid-fast Cell Walls • Similar to Gram-positive structure, buthave Mycolic Acid: A waxy lipid • Require special acid-fast staining technique • Includes Mycobacterium and Nocardia

  14. IV. B. 2.     Cell Wall • Variations on Cell Wall Architecture (cont.) • Mycoplasmas • Bacteria that are naturally have no cell walls • Includes Mycoplasma and Ureaplasma • Archaeobacteria • Have unusual archaeobacterial cell wallswith no peptidoglycan • Have unusual metabolisms • Share a more recent common ancestor with eukaryotes than with eubacteria (“true bacteria”)

  15. IV. B. 3.     Plasma Membrane • Structure • Phospholipid Bilayer with Associated Proteins • Functions • Maintain Cell Integrity • Regulate Transport • Specialized Functions in Bacteria

  16. IV. B. 4. Cytoplasm & Cytoplasmic Inclusions • Composition: • Viscous aqueous suspension of proteins, nucleic acid, dissolved organic compounds, mineral salts • Cytoplasmic Inclusions: • Metachromatic Granules (Phosphate) • Starch Granules • Lipid Droplets • Sulfur Granules

  17. IV. B. 5.     Ribosomes • Suspended in Cytoplasm • Sites of Protein Synthesis

  18. IV. B. 6.     Bacterial DNA • Chromosomal DNA • Plasmid DNA • R-Plasmids • F-Plasmids

  19. IV. B. 7.     Pili • Hair-like structures on cell surface • Functions • Attachment • Conjugation

  20. IV. B. 8.     Flagella • Function • MotilityAlmost all motile bacteria are motile by means of flagella • Motile vs. nonmotile bacteria • Structure • FilamentComposed of the protein flagellin • Hook & Rotor AssemblyPermits rotational "spinning" movement

  21. IV. B. 8.     Flagella • Mechanism of Motility • “Run and Tumble” Movementcontrolled by the direction of the flagellar spin • Counterclockwise spin = Straight RunClockwise spin = Random Tumble

  22. IV. B. 8.     Flagella • Chemotaxis • Response to the concentration of chemical attractants and repellants • As a bacterium approaches an attractant:the lengths of the straight runs increase • As a bacterium approaches a repellant:the lengths of the straight runs decrease

  23. IV. B. 9.     Spores • Function • To permit the organism to survive during conditions of desiccation, nutrient depletion, and waste buildup • Bacterial spores are NOT a reproductive structure, like plant or fungal spores • Occurrence • Produced by very few genera of bacteria • Major examplesBacillusClostridium

  24. IV. B. 9.     Spores • Significance in Medicine & Industry • Spores are resistant to killing • Cannot be killed by 100°C (boiling) • Requires heating to 120°C for 15-20 min (autoclaving or pressure cooking)

  25. IV. B. 9.     Spores • Sporulation • The process of spore formation • Governed by genetic mechanism • A copy of the bacterial chromosome is surrounded by a thick, durable spore coat • This forms an endospore within a vegetative cell • When the vegetative cell dies and ruptures, the free spore is released

  26. IV. B. 9.     Spores • Spore Germination • When a spore encounters favorable growth conditions • The spore coat ruptures and a new vegetative cell is formed

  27. IV. C. Factors that Influence Bacterial Growth • Growth vs. Survival • Bacteria may tolerate or survive under more extreme conditions than their growth conditions

  28. IV. C. Factors that Influence Bacterial Growth • Nutrient Requirements • Energy SourceMost bacteria are chemotrophs; a few are phototrophs • Carbon SourceMost bacteria are heterotrophs; a few are autotrophs • Nitrogen, Phosphate, Sulfur, Trace Minerals

  29. IV. C. Factors that Influence Bacterial Growth • Nutrient Requirements (cont.) • Special Requirements examples: amino acids and enzyme cofactors (vitamins) Fastidious bacteria: Strains that are difficult or impossible to culture due to special growth requirements

  30. IV. C. Factors that Influence Bacterial Growth • Temperature • PsychrophilesGrow at ~0°C - 20°C • Mesophiles Grow at ~20°C - 45°C • Moderate Thermophiles Grow at ~45°C - 70°C • Extreme Thermophiles Grow at ~70°C - 100°C

  31. IV. C. Factors that Influence Bacterial Growth • pH • Acidophiles Grow at ~pH 1.0 - pH 6.0 • Neutrophiles Grow at ~pH 6.0 - pH 8.5 • Alkalophiles Grow above pH 8.5

  32. IV. C. Factors that Influence Bacterial Growth • Oxygen • Strict aerobes (Obligate aerobes) Use oxygen for respiration in their metabolismRequire the presence of a normal oxygen concentration (~20%) for growth • Strict anaerobes (Obligate anaerobes) Oxygen is a poison for these microbes Cannot grow at all in the presence of oxygen

  33. IV. C. Factors that Influence Bacterial Growth • Oxygen (cont.) • Aerotolerate anaerobes Do not use oxygen, but oxygen is not a poison for these Can grow equally well with or without oxygen • Facultative anaerobes Use oxygen for respiration, but can also grow without oxygen Grow better with oxygen that without oxygen

  34. IV. C. Factors that Influence Bacterial Growth • Oxygen (cont.) • Microaerophiles Require low concentrations (~5% - 10%) of oxygen for growth

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