Download - MICRO06 Lect 4
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The ProkaryotesThe Prokaryotes
Sofronio Agustin
Professor
Sofronio Agustin
Professor
LECTURES IN MICROBIOLOGYLECTURES IN
MICROBIOLOGY
LESSON 4LESSON 4
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Lesson 4 TopicsLesson 4 Topics
External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification
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External StructuresExternal Structures
Flagella
Pili and fimbriae
Glycocalyx
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FlagellaFlagella
Composed of protein subunits called flagellin.
“H” antigens used in serotyping of bacterial
strains. Example: Escherichia coli O157: H7
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Flagellar StructureFlagellar Structure
Three components of a flagellum: filament, hook and basal body
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Flagellar ArrangementFlagellar Arrangement
(a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous
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Bacterial MotilityBacterial Motility
The rotation of the flagella enables bacteria to be motile.
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ChemotaxisChemotaxis
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.
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EndoflagellaEndoflagella
Spirochetes have their
flagella embedded in the
membrane = endoflagella
Also called axial filament
Example: T. pallidum
(corkscrew motility)
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Pili and FimbriaePili and Fimbriae
Attachment
Mating (Conjugation)
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FimbriaeFimbriae
Fimbriae are smaller than flagella and are important for attachment.
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Pili Pili
Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).
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Glycocalyx
CapsuleProtects bacteria from phagocytic cells
Slime layerEnable attachment and aggregation of bacterial cells
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CapsuleCapsule
The capsule is covalently
bound to the cell wall.
Associated with virulence in bacteria.
Example:
Streptococcus pneumoniae
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Slime LayerSlime 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”
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Biofilms Biofilms
The slime layer is associated with cell aggregation and the formation of biofilms
Example:Staphylococcus epidermidis biofilms on catheter tips
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Cell EnvelopeCell Envelope
Cell wallGram-positive
Gram-negative
Cytoplasmic membrane Cell wall-less bacteria
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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
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Peptidoglycan Layer Peptidoglycan Layer
PG is a complex sugar and peptide structure important for cell wall stability and shape.
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Cell Wall Structures Cell Wall Structures
Structures associated with gram-positive and gram-negative cell walls.
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Cytoplasmic MembraneCytoplasmic Membrane
Phospholipid bilayer “Fluid mosaic” model
Embedded proteins for active transport
Enzymes for energy generation
Photosynthetic pigments
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L FormsL Forms
Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.
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Cell Wall Less Bacteria Cell Wall Less Bacteria
No peptidoglycan layer
Cell membrane contains sterols for stability
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The MycoplasmaThe Mycoplasma
Mycoplasma bacteria
have no cell wall, which
contributes to their
pleomorphic shapes
Smallest bacteria (0.2 um)
Example:Mycoplasma pneumoniae (SEM on right)
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Internal Structures
Cytoplasm Genome Inclusion bodies Actin Endospore
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CytoplasmCytoplasm
Gelatinous solution containing water,
nutrients, proteins, and genetic material
Site for cell metabolism
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Genetic StructuresGenetic Structures
Deoxyribonucleic acid (DNA)
Ribonucleic acid (RNA)
Ribosomes
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Bacterial Genome Bacterial Genome
Most bacteria contain a single circular double strand of DNA called a nucleoid.
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Prokaryotic RibosomeProkaryotic 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
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Inclusion BodiesInclusion Bodies
Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments
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Bacterial CytoskeletonBacterial Cytoskeleton
Actin is a protein fiber present in some bacteria, which is involved in maintaining cell shape.
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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
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Endospore FormationEndospore Formation
Some pathogenic bacteria that produce toxins during the vegetative stage are capable of forming spores. (e.g. Bacillus and Clostridium species)
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Bacterial MorphologyBacterial Morphology
Coccus Rod or bacillus Curved or spiral Cell arrangements Pleomorphism
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Typical Shapes and ArrangementsTypical Shapes and Arrangements
Scanning electron micrographs of different bacterial shapes and arrangements.
(a) Streptococcus (b) Bacillus (c) Spirochete (d) Spirillum
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PleomorphismPleomorphism
Some bacteria show varied shapes and arrangements called pleomorphism. Ex: Corynebacterium diphtheriae’s “Chinese letter” arrangement.
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Bacterial Shapes and Arrangements Bacterial Shapes and Arrangements
Cellular shapes and arrangements are useful in bacterial identification.
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The Dimension of Bacteria The Dimension of Bacteria
Relative size of a bacterial cell compared to other cells including viruses.
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ClassificationClassification
Phenotypic methods
Molecular methods
Taxonomic scheme Unique groups
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Phenotypic MethodsPhenotypic Methods
Cell morphology - staining Biochemical test – enzyme test
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Molecular MethodsMolecular Methods
DNA sequence 16S RNA Protein sequence
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Major Taxonomic Groups of BacteriaMajor 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)
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Unique Bacterial TypesUnique Bacterial Types
Intracellular bacteria
Photosynthetic bacteria
Sulfur bacteria
Gliding and fruiting bacteria
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Intracellular BacteriaIntracellular Bacteria
Intracellular bacteria
must live in host cells for
them to metabolize and
reproduce
Examples:
Rickettsiae
and Chlamydiae
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CyanobacteriaCyanobacteria
Cyanobacteria are important photosynthetic bacteria associated with oxygen production.
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Sulfur BacteriaSulfur Bacteria
Green and purple sulfur bacteria are photosynthetic, do not give off oxygen, and are found in sulfur springs, freshwater, and swamps.
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MyxobacteriaMyxobacteria
An example of a fruiting body bacteria in which reproductive spores are produced.
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ArchaeaArchaea
Associated with extreme environments Contain unique cell walls Contain unique internal structures
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ArchaeaArchaea
Archaea are found in:
hot springs (thermophiles) high salt content areas (halophiles)
Example:Halobacterium salinarium