The prokaryotes
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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.

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The prokaryotes

LECTURES IN

MICROBIOLOGY

The Prokaryotes

Sofronio Agustin

Professor

LESSON 4


Lesson 4 topics

Lesson 4 Topics

  • External Structures

  • Cell Envelope

  • Internal Structures

  • Cell Shapes, Arrangement, and Sizes

  • Classification


External structures

External Structures

  • Flagella

  • Pili and fimbriae

  • Glycocalyx


Flagella

Flagella

  • Composed of protein subunits called flagellin.

  • “H” antigens used in serotyping of bacterial strains.

  • Example: Escherichia coli O157: H7


Flagellar structure

Flagellar Structure

Three components of a flagellum: filament, hook and basal body


Flagellar arrangement

Flagellar Arrangement

(a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous


Bacterial motility

Bacterial Motility

The rotation of the flagella enables bacteria to be motile.


Chemotaxis

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.


Endoflagella

Endoflagella

  • Spirochetes have their flagella embedded in the membrane = endoflagella

  • Also called axial filament

  • Example: T. pallidum (corkscrew motility)


Pili and fimbriae

Pili and Fimbriae

  • Attachment

  • Mating (Conjugation)


Fimbriae

Fimbriae

Fimbriae are smaller than flagella and are important for attachment.


The prokaryotes

Pili

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


Glycocalyx

Glycocalyx

  • Capsule

    Protects bacteria from phagocytic cells

  • Slime layer

    Enable attachment and aggregation of bacterial cells


Capsule

Capsule

  • The capsule is covalently bound to the cell wall.

  • Associated with virulence in bacteria.

  • Example:

    Streptococcus pneumoniae


Slime layer

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”


Biofilms

Biofilms

  • The slime layer is associated with cell aggregation and the formation of biofilms

  • Example:

    Staphylococcus epidermidis biofilms on catheter tips


Cell envelope

Cell Envelope

  • Cell wall

    Gram-positive

    Gram-negative

  • Cytoplasmic membrane

  • Cell wall-less bacteria


Cell wall

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


Peptidoglycan layer

Peptidoglycan Layer

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


Cell wall structures

Cell Wall Structures

Structures associated with gram-positive and gram-negative cell walls.


Cytoplasmic membrane

Cytoplasmic Membrane

  • Phospholipid bilayer

  • “Fluid mosaic” model

  • Embedded proteins for active transport

  • Enzymes for energy generation

  • Photosynthetic pigments


L forms

L Forms

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


Cell wall less bacteria

Cell Wall Less Bacteria

  • No peptidoglycan layer

  • Cell membrane contains sterols for stability


The mycoplasma

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)


Internal structures

Internal Structures

  • Cytoplasm

  • Genome

  • Inclusion bodies

  • Actin

  • Endospore


Cytoplasm

Cytoplasm

  • Gelatinous solution containing water, nutrients, proteins, and genetic material

  • Site for cell metabolism


Genetic structures

Genetic Structures

  • Deoxyribonucleic acid (DNA)

  • Ribonucleic acid (RNA)

  • Ribosomes


Bacterial genome

Bacterial Genome

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


Prokaryotic ribosome

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


Inclusion bodies

Inclusion Bodies

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


Bacterial cytoskeleton

Bacterial Cytoskeleton

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


Endospores

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


Endospore formation

Endospore Formation

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


Bacterial morphology

Bacterial Morphology

  • Coccus

  • Rod or bacillus

  • Curved or spiral

  • Cell arrangements

  • Pleomorphism


Typical shapes and arrangements

Typical Shapes and Arrangements

Scanning electron micrographs of different bacterial shapes and arrangements.

(a) Streptococcus (b) Bacillus (c) Spirochete (d) Spirillum


Pleomorphism

Pleomorphism

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


Bacterial shapes and arrangements

Bacterial Shapes and Arrangements

Cellular shapes and arrangements are useful in bacterial identification.


The dimension of bacteria

The Dimension of Bacteria

Relative size of a bacterial cell compared to other cells including viruses.


Classification

Classification

  • Phenotypic methods

  • Molecular methods

  • Taxonomic scheme

  • Unique groups


Phenotypic methods

Phenotypic Methods

  • Cell morphology - staining

  • Biochemical test – enzyme test


Molecular methods

Molecular Methods

  • DNA sequence

  • 16S RNA

  • Protein sequence


Major taxonomic groups of bacteria

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)


Unique bacterial types

Unique Bacterial Types

  • Intracellular bacteria

  • Photosynthetic bacteria

  • Sulfur bacteria

  • Gliding and fruiting bacteria


Intracellular bacteria

Intracellular Bacteria

  • Intracellular bacteria must live in host cells for them to metabolize and reproduce

  • Examples:

    Rickettsiae

    and Chlamydiae


Cyanobacteria

Cyanobacteria

Cyanobacteria are important photosynthetic bacteria associated with oxygen production.


Sulfur bacteria

Sulfur Bacteria

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


Myxobacteria

Myxobacteria

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


Archaea

Archaea

  • Associated with extreme environments

  • Contain unique cell walls

  • Contain unique internal structures


Archaea1

Archaea

  • Archaea are found in:

  • hot springs (thermophiles)

  • high salt content areas (halophiles)

  • Example:

    Halobacterium salinarium


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