1. Chair of Medical Biology, Microbiology, Virology, and Immunology CELL STRUCTURE OF BACTERIA. Lecturer As. Prof. O. Pokryshko

2. The Dimension of Bacteria Relative size of a bacterial cell compared to other cells including viruses.

3. Bacterial surface structures

4. Cell Envelope  Cytoplasmic membrane  Cell wall Cell wall-less bacteria  No peptidoglycan layer  Cell membrane contains sterols for stability Mycoplasma pneumoniae

5. Cytoplasmic Membrane  Phospholipid bilayer  “Fluid mosaic” model  Embedded proteins for active transport  Enzymes for energy generation  Photosynthetic pigments

6. Cell membrane Peripheral Membrane Protein Integral Membrane Protein Peripheral Membrane Protein Phospholipid

7. Selective permeability to different molecules. Selective permeability to different molecules. Active transport aided by permease. Active transport aided by permease. Play a role in DNA replication. Play a role in DNA replication. Cell wall biosynthesis. Cell wall biosynthesis. Mesosomes ----- cell division. Mesosomes ----- cell division. Function of Cytoplasmic Membrane

8. Cell wall Two major groups of bacteria based on structure of cell wall Two major groups of bacteria based on structure of cell wall Gram positive Gram positive Thick peptidoglycan layer Thick peptidoglycan layer Gram negative Gram negative Thin peptidoglycan layer Thin peptidoglycan layer Outer membrane containing LPS Outer membrane containing LPS Gram stain is crucial first step toward identification Gram stain is crucial first step toward identification

9. Peptidoglycan (cell wall)

10. Cell Wall  Gram positive cell wall Thick peptidoglycan (PG) layer Thick peptidoglycan (PG) layer Acidic polysaccharides Acidic polysaccharides Teichoic acid and lipoteichoic acid Teichoic acid and lipoteichoic acid  Gram-negative cell wall Thin peptidoglycan (PG) layer Thin peptidoglycan (PG) layer Lipopolysaccharide layer Lipopolysaccharide layer Porins Porins Periplasmic space Periplasmic space

11. Gram-positive cell envelope

12. Gram-negative cell envelope

13. Cell Wall Structures Structures associated with gram-positive and gram-negative cell walls.

14. Maintenance of the shape (due to rigidity of peptidoglycan). Maintenance of the shape (due to rigidity of peptidoglycan). Protects the cytoplasmic membrane cell contents Protects the cytoplasmic membrane cell contents Rigidity Rigidity Cell wall is osmotically insensitive Cell wall is osmotically insensitive Hypotonic solution – cell burst. Hypotonic solution – cell burst. Hypertonic solution – cell shrank. Hypertonic solution – cell shrank. Isotonic solution – bacteria is life. Isotonic solution – bacteria is life. Function of Cell Wall

15. L Forms Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.

16. Capsules are important for are important for Adhesion Adhesion (Associated with virulence in bacteria) Avoidance of immune response Avoidance of immune response (Protects bacteria from phagocytic cells) Protection from dehydration Protection from dehydration

17. Capsule Klebsiella pneumoniae Bacillus anthracis Streptococcus pneumoniae

18. External structures Pili ( play roles in Pili ( Fimbriae) play roles in Adhesion Adhesion Exchange of genetic material Exchange of genetic material Avoidance of immune response Avoidance of immune response Flagella are important for Flagella are important for Motility (dispersal) Motility (dispersal) Antigenic determinant ( Number and location species specific Antigenic determinant ( “H” antigens) Number and location species specific

19. Pili and flagella Salmonella Fimbriae are smaller than flagella and are important for attachment.

20. PiliPili Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).

21. Flagellar Structure Three components of a flagellum: filament, hook and basal body It composed of protein subunits called flagellin.

22. Flagellar Arrangement (a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous

23. Bacterial Motility The rotation of the flagella enables bacteria to be motile.

24.  Cytoplasm  Genome  Inclusion bodies  Endospore Internal Structures

25. CytoplasmCytoplasm  Gelatinous solution containing water, nutrients, proteins, and genetic material  Site for cell metabolism

26. 26 Chemical Analysis of Microbial Cytoplasm 70% water 70% water Proteins Proteins 96% of cell is composed of 6 elements: 96% of cell is composed of 6 elements: carbon carbon hydrogen hydrogen oxygen oxygen phosphorous phosphorous sulfur sulfur nitrogen nitrogen

27. Bacterial Genome Most bacteria contain a single circular double strand of DNA called a nucleoid.

28. Prokaryotic Ribosome  A ribosome is a combination of RNA and protein, and is the site for protein synthesis  Composed of large (50S) and small (30S) subunits  S = Svedverg unit, measures molecular size

29. Inclusion Bodies Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments

30. Some bacteria, notably those of the genera Bacillus and Clostridium, develop a highly resistant resting phase or endospore that does not grow or reproduce and exhibit absolute dormancy (not detectable metabolism). Some bacteria, notably those of the genera Bacillus and Clostridium, develop a highly resistant resting phase or endospore that does not grow or reproduce and exhibit absolute dormancy (not detectable metabolism). Bacterial Spores

31. Endospores Bacillus anthracis

32. Vegatitive form Vegatitive form The bacteria actively growing, non spore stage of a bacterium. The bacteria actively growing, non spore stage of a bacterium. Sporulation: Sporulation: Formed on exposure to unfavorable condition,E.g., Formed on exposure to unfavorable condition,E.g., Nutrient depletion Nutrient depletion Changes Changes Moisture, Moisture, Temperature, Temperature, pH or pH or Oxygen tension Oxygen tension Spore requires 10-15 hours to form. Spore requires 10-15 hours to form.

33. Endospore formation

34. Germination Mature endoscope are metabolically inert Mature endoscope are metabolically inert Changes in the environment Changes in the environment Retuning to vegetative state within 15 minutes. Retuning to vegetative state within 15 minutes. In the process of germination the spores absorb water and swell, the protective coat disintegrates and a single vegatitive cell emerges. In the process of germination the spores absorb water and swell, the protective coat disintegrates and a single vegatitive cell emerges.