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Morphology and str.of bacteria
- 4. Bacterial Cell wall Tough and rigid stracture,surrounding bacterium 10-25 nm thick Weighs 20-25% of dry weight of cell. Peptido-glycan Polymer (amino acids + sugars) Unique to bacteria
- 5. Continue… FUNCTIONS: 1. Protection 2. confers rigidity 3. accounts for shape of bacteria 4. takes part in cell division 5. site of action of several antibiotics 6. contains virulence factor
- 6. Gram positive and gram negative bacterial cell wall. characters Gram negative cell wall Gram positive cell wall Gram reaction pstain red or pink Stains blue or purple Peptidoglycan layer Thin (single-layered) Thick (multilayered) Teichoic acids Absent Present in many Periplasmic space present Absent Outer membrane Present Absent Lipopolysaccharide (LPS) content High Virtually none Lipid and lipoprotein content High (due to presence of outer membrane) Low (acid-fast bacteria have lipids linked to peptidoglycan)
- 7. Continue…Mesosome Mesosome is less prominent. Mesosome is more prominent. Toxins produced Primarily Endotoxins Primarily Exotoxins Resistance to physical disruption Low High Susceptibility to anionic detergents Low High Cell wall composition The cell wall is 70-120 Å (ångström) thick; two layered. Lipid content is 20-30% (high), Murein content is 10-20% (low). The cell wall is 100-120 Å thick; single layered. Lipid content of the cell wall is low , whereas Murein content is 70- 80% (higher). Antibiotic Resistance More resistant to antibiotics. More susceptible to antibiotics
- 9. Outer membrane: Phospholipid layer ouside to thin peptidoglycan layer Protective barrier to cell wall Prevents loss of constituents
- 10. Cytoplasm matrix 80% Water {20% Salts-Proteins) Osmotic Shock important DNA is circular, Haploid Advantages of 1N DNA over 2N DNA More efficient; grows quicker Mutations allow adaptation to environment quicker Plasmids; extra circular DNA Antibiotic Resistance No organelles (Mitochondria, Golgi, etc.)
- 11. CELL MEMBRANE/PLASMA MEMBRANE Fluid mosac model is accepted model to describe its stracture 5-10 nm thick Essential for survival of bacteria Bilayer Phospholipid Site for metabolic proceses Water can penetrate Flexible Not strong, ruptures easily Osmotic Pressure created by cytoplasm
- 12. fluid mosaic model of a cell membrane
- 13. Nucleoid Lack true nucleus Genetic material is located in irregularly shaped region called nucleoid. No nuclear membrane or nucleolus Also bacteria posses extracellular DNA called plasmids DNA divide by binary fossion Posses super coiled circular ds DNA of 1mm length.
- 14. Capsule and slime layer Some bacteria posses a layer of viscous material lying outside the cell wall called glycocalyx. When this glycocalyx layer is well organized not easily washed off it is called Capsule When this layer is thin in form of loose material that can be washed easily it is called slime layer
- 15. Function/uses Contribute to bacterial virulence Protects bacteria from phagocytosis Prevent cell from drying Prevents from action of lysozyme and bacteriophages Biofilm formation and adhension Source of nutrients Capsule as vaccine
- 17. FLAGELLA Flagellum (singular) is hair like helical structure emerges from cell wall and cell membrane It is responsible for motility of the bacteria Size: thin 15-20nm in diameter. Flagella is not straight but is helical. It is composed of flagellin protein (globular protein) and known as H antigen. Flagella has three parts. Basal body, Hook and filament
- 18. Arrangement basis for classification Monotrichous; 1 flagella Lophotrichous; tuft at one end Amphitrichous; both ends Peritrichous; all around bacteria
- 19. Fimbriae or pili: Fimbriae and Pili are filamentous structures composed of protein (Pilin) that extend from the surface of a cell and can have many functions. Fimbriae are found in gram negative as well as gram positive bacteria but are shorter in length as compared to pili. Pili are longer than fimbriae and there are only a few per cell.
- 21. Pili Characteristics Fimbriae Pili Definition Fimbriae are tiny bristle- like fibers arising from the surface of bacterial cells. Pili are hair like microfibers that are thick tubular structure made up of pilin. Length Shorter than pili Longer than fimbriae. Diameter Thin Thicker than fimbriae. Number No. of fimbriae are 200- 400 per cell. No of pili are less 1-10 per cell. Made up of Fimbrillin protein. Pilin protein. Found in Both gram positive and gram negative bacteria. Only gram negative bacteria.
- 22. Function Responsible for cell to surface attachment. Specialized for attachment i.e. enable the cell to adhere the surfaces of other bacteria. Responsible for bacterial conjugation. Two basic function of pili. They are gene transfer and attachment. Motility Do not function in active motility. Type IV pili shows twitching type of motility. Receptors No receptors of other. Serve as receptor for certain viruses. Examples Salmonella typhimurium, Shigella dysenteriae. Escherichia coli, Neisseria gonorrhoeae.
- 23. Bacterial spores These are dormant form of bacteria ,which are thick walled and highly resistant . Spore formation (sporulation) occurs when nutrients, such as sources of carbon and nitrogen are depleted. These are formed in unfavorable environmental conditions . Bacterial spores formed within the parent cell are called endospores. Sporulation (or sporogenesis) refers to process of formation of spores from vegetative stage. Germination is the transformation of dormant spore into active vegetative cell.
- 24. Bacterial spores are highly resistant to Heat Dehydration Radiation and Chemicals. Examples of Spore forming Bacteria- Bacillus spp Clostridium spp
- 25. Structure of spore It comprises of several layers. From innermost to the outermost the layers are: Core → Cortex → Coat → Exosporum
- 26. Thanks…