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LECTURES IN MICROBIOLOGY. The Prokaryotes. Sofronio Agustin Professor. LESSON 4. Lesson 4 Topics. External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification. External Structures. Flagella Pili and fimbriae Glycocalyx. Flagella. - PowerPoint PPT Presentation
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The Prokaryotes
Sofronio AgustinProfessor
LECTURES IN MICROBIOLOGY
LESSON 4
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
Flagellar Structure
Three components of a flagellum: filament, hook and basal body
6
Flagellar Arrangement
(a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous
7
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
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
CapsuleProtects bacteria from phagocytic cells
Slime layerEnable 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 wallGram-positive
Gram-negative
Cytoplasmic membrane Cell wall-less bacteria
18
Cell Wall
Gram positive 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
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
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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
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