1. Sofronio Agustin Professor
LECTURES IN
MICROBIOLOGY
The Prokaryotes
LESSON 4
Sofronio Agustin
Professor

2. Lesson 4 Topics External Structures Cell Envelope Internal Structures
Cell Shapes, Arrangement, and Sizes
Classification

3. External Structures
Flagella
Pili and fimbriae
Glycocalyx

4. Flagella Composed of protein subunits called flagellin.
“H” antigens used in serotyping of bacterial strains.
Example: Escherichia coli O157: H7

5. Three components of a flagellum: filament, hook and basal body
Flagellar Structure
Three components of a flagellum: filament, hook and basal body

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

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

8. Chemotaxis
Chemotaxis is the movement of bacteria in response to chemical signals. It consists of a series of tumbles and runs toward or away from source of stimuli.

9. Endoflagella
Spirochetes have their flagella embedded in the membrane = endoflagella
Also called axial filament
Example: T. pallidum (corkscrew motility)

10. Pili and Fimbriae
Attachment
Mating (Conjugation)

11. Fimbriae are smaller than flagella and are important for attachment.

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

13. Glycocalyx Capsule Slime layer Protects bacteria from phagocytic cells
Enable attachment and aggregation of bacterial cells

14. Capsule The capsule is covalently bound to the cell wall.
Associated with virulence in bacteria.
Example:
Streptococcus pneumoniae

15. Slime Layer The slime layer is loosely bound to the cell.
Carbohydrate rich material enhances adherence of cells on surfaces
Example:
Streptococcus mutans and “plaque formation”

16. Biofilms
The slime layer is associated with cell aggregation and the formation of biofilms
Example:
Staphylococcus epidermidis biofilms on catheter tips

17. Cell Envelope Cell wall Cytoplasmic membrane Cell wall-less bacteria
Gram-positive
Gram-negative
Cytoplasmic membrane
Cell wall-less bacteria

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

19. Peptidoglycan Layer
PG is a complex sugar and peptide structure important for cell wall stability and shape.

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

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

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

23. Cell Wall Less Bacteria
No peptidoglycan layer
Cell membrane contains sterols for stability

24. The Mycoplasma
Mycoplasma bacteria have no cell wall, which contributes to their pleomorphic shapes
Smallest bacteria
(0.2 um)
Example:
Mycoplasma pneumoniae
(SEM on right)

25. Internal Structures
Cytoplasm
Genome
Inclusion bodies
Actin
Endospore

26. Cytoplasm
Gelatinous solution containing water, nutrients, proteins, and genetic material
Site for cell metabolism

27. Genetic Structures Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA)
Ribosomes

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

29. 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

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

31. Bacterial Cytoskeleton
Actin is a protein fiber present in some bacteria, which is involved in maintaining cell shape.

32. Endospores
Nutrient depletion induces some bacteria (vegetative cell) to form endospores in order to survive
Dehydrated gel state due to calcium-protein complex
Dipicolinic acid (found only in spores) hardens the spore

33. Endospore Formation
Some pathogenic bacteria that produce toxins during the vegetative stage are capable of forming spores. (e.g. Bacillus and Clostridium species)

34. Bacterial Morphology Coccus Rod or bacillus Curved or spiral
Cell arrangements
Pleomorphism

35. Typical Shapes and Arrangements
Scanning electron micrographs of different bacterial shapes and arrangements.
(a) Streptococcus (b) Bacillus (c) Spirochete (d) Spirillum

36. Pleomorphism
Some bacteria show varied shapes and arrangements called pleomorphism. Ex: Corynebacterium diphtheriae’s “Chinese letter” arrangement.

37. Bacterial Shapes and Arrangements
Cellular shapes and arrangements are useful in bacterial identification.

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

39. Classification Phenotypic methods Molecular methods Taxonomic scheme
Unique groups

40. Phenotypic Methods Cell morphology - staining
Biochemical test – enzyme test

41. Molecular Methods
DNA sequence
16S RNA
Protein sequence

42. Major Taxonomic Groups of Bacteria
The methods of classification have allowed bacteria to be classified into different taxonomic groups
Re: Bergey’s Manual of Determinative Bacteriology
(Table on right)

43. Unique Bacterial Types
Intracellular bacteria
Photosynthetic bacteria
Sulfur bacteria
Gliding and fruiting bacteria

44. Intracellular Bacteria
Intracellular bacteria must live in host cells for them to metabolize and reproduce
Examples:
Rickettsiae
and Chlamydiae

45. Cyanobacteria
Cyanobacteria are important photosynthetic bacteria associated with oxygen production.

46. Sulfur Bacteria
Green and purple sulfur bacteria are photosynthetic, do not give off oxygen, and are found in sulfur springs, freshwater, and swamps.

47. Myxobacteria
An example of a fruiting body bacteria in which reproductive spores are produced.

48. Archaea Associated with extreme environments Contain unique cell walls
Contain unique internal structures

49. Archaea Archaea are found in: hot springs (thermophiles)
high salt content areas (halophiles)
Example:
Halobacterium salinarium