1 / 38

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

niveditha
Download Presentation

IV. Bacterial Structure and Growth

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related