Microbiology: A Systems Approach Chapter 4 Procaryotic Profiles: The Bacteria and Archaea PowerPoint...
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Transcript of Microbiology: A Systems Approach Chapter 4 Procaryotic Profiles: The Bacteria and Archaea PowerPoint...
Microbiology: A Systems Approach
Chapter 4Procaryotic Profiles:
The Bacteria and Archaea
PowerPoint to accompany
Cowan/Talaro
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Chapter 4
Topics– Cell Shapes, Arrangement, and Sizes – External Structures– Cell Envelope– Internal Structures– Classification
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Relative size of a bacterial cell compared to other cells including viruses.
Fig. 4.25 The dimension of bacteria
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Cell shapes
• Coccus• Rod or bacillus• Curved or spiral• Cell arrangements
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Scanning electron micrographs of different bacterial shapes and arrangements.
Fig. 4.23 SEM photograph of basic shapes.
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Cellular shapes and arrangements are specific characteristics that can be used to identify bacteria.
Fig. 4.22 Bacterial shapes and arrangements
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Some bacteria (ex. Corynebacterium) have varied shapes called pleomorphism.
Fig. 4.24 Pleomorphism in Corynebacterium
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External Structures
• Flagella• Pili and fimbriae• Glycocalyx
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Flagella
• Composed of protein subunits• Motility (chemotaxis)• Varied arrangement (ex.
Monotrichous, lophotrichous, amphitrichous)
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Different arrangements of flagella exist for different species.
Fig. 4.3 Electron micrograph depicting types of flagella arrangements.
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Three main parts of the flagella include the basal body, hook, and filament.
Fig. 4.2 Details of the basal body in gram negative cell
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The rotation of the flagella enables bacteria to be motile.
Fig. 4.4 The operation of flagella and the mode of locomotion in bacteria with polar and peritrichous flagella.
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Chemotaxis is the movement of bacteria in response to chemical signals.
Fig. 4.5 Chemotaxis in bacteria
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Spirochete bacteria have their flagella embedded in the membrane.
Fig. 4.6 The orientation of periplasmic flagella on the spirochete cell.
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Pili and fimbriae
• Attachment• Mating (Conjugation)
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Fimbriae are smaller than flagella, and are important for attachment.
Fig. 4.7 Form and function of bacteria fimbriae
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Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another.
Fig. 4.8 Three bacteria in the process of conjugating
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Glycocalyx
• Capsule– Protects bacteria from immune cells
• Slime layer– Enable attachment and aggregation
of bacterial cells
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The capsule is tightly bound to the cell, and is associated with pathogenic bacteria.
Fig. 4.10 Encapsulated bacteria
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The slime layer is loosely bound to the cell.
Fig. 4.9 Bacterial cells sectioned to show the typesof glycocalyces.
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The slime layer is associated with the formation of biofilms, which are typically found on teeth.
Fig. 4.11 Biofilm
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Cell envelope
• Cell wall– Gram-positive – Gram-negative
• Cytoplasmic membrane • Non cell wall
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Cell wall
• Gram positive cell wall– Thick peptidoglycan (PG) layer– Teichoic acid and lipoteichoic acid– Acidic polysaccharides– Lipids – mycolic acids - Mycobacteria
• Gram-negative cell wall– Thin PG layer– Outer membrane– Lipid polysaccharide– Porins
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PG is a complex sugar and peptide structure important for cell wall stability and shape.
Fig. 4.13 Structure of peptidoglycan in the cell wall
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Structures associated with gram-positive and gram-negative cell walls.
Fig. 4.14 A comparison of the detailed structure of gram-positive and gram-negative cell walls.
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Mutations can cause some bacteria to lose the ability to synthesize the cell wall, and are called L forms.
Fig. 4.16 The conversion of walled bacterial cells to L forms
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No cell wall
• No PG layer• Cell membrane contain sterols for
stability
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Mycoplasma bacteria have no cell wall, which contributes to varied shapes.
Fig. 4.15 Scanning electron micrograph of Mycoplasma pneumoniae
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Cytoplasmic membrane
• Fluid-Mosaic Model• Phospholipids• Embedded proteins• Energy generation• Selective barrier; semipermeable• Transport
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Internal Structures
• Cytoplasm• Genetic structures • Storage bodies• Actin• Endospore
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Cytoplasm
• Area inside the membrane• About 80% water• Gelatinous solution containing
water, nutrients, proteins, and genetic material.
• Site for cell metabolism
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Genetic structures
• Single, circular chromosome• Nucleoid region• Deoxyribonucleic acid (DNA)• Ribonucleic acid (RNA)• Plasmids• Ribosomes
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Most bacteria contain a single circular double strand of DNA called a chromosome.
Fig. 4.17 Chromosome structure
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A ribosome is a combination of RNA and protein, and is involved in protein synthesis.
Fig. 4.18 A model of a procaryotic ribosome.
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Inclusion bodies enable a cell to store nutrients, and to survive nutrient depleted environments.
Fig. 4.19 An example of a storage inclusionin a bacterial cell.
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Actin is a protein fiber (cytoskeleton) present in some bacteria, and is involved in maintaining cell shape.
Fig. 4.20 Bacterial cytoskeleton
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During nutrient depleted conditions, some bacteria (vegetative cell) form into an endospore in order to survive.
Fig. 4.21 Microscopic picture of an endospore formation
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Some pathogenic bacteria that produce toxins during the vegetative stage are capable of forming spores.
Table 4.1 General stages in endospore formation
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Classification
• Phenotypic methods• Molecular methods• Taxonomic scheme• Unique groups
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Phenotypic methods
• Cell morphology -staining• Biochemical test – enzyme test
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Molecular methods
• DNA sequence• 16S RNA• Protein sequence
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The methods of classification have allowed bacteria to be grouped into different divisions and classes.
Table 4.3 Major taxonomic groups of bacteria
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An example of how medically important families and genera of bacterial are characterized.
Table 4.4 Medically important families and genera of bacteria.
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Unique groups of bacteria
• Intracellular parasites• Photosynthetic bacteria• Green and purple sulfur bacteria• Gliding and fruiting bacteria• Archaea bacteria
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Intracellular bacteria must live in host cells in order to undergo metabolism and reproduction.
Fig. 4.26 Transmission electron micrograph of rickettsia.
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Cyanobacteria are important photosynthetic bacteria associated with oxygen production.
Fig. 4.27 Structure and examples of cyanobacteria
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Green and purple sulfur bacteria are photosynthetic, do not give off oxygen, and are found in sulfur springs, freshwater, and swamps.
Fig. 4.28 Behavior of purple sulfur bacteria
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An example of a fruiting body bacteria in which reproductive spores are produced.
Fig. 4.29 Myxobacterium
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Archaea bacteria
• Associated with extreme environments
• Contain unique cell walls• Contain unique internal structures
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Archaea bacteria that survive are found in hot springs (thermophiles) and high salt content areas (halophiles).
Fig. 4.30 Halophile around the world