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Cell Walls of Archaea
- - trade peptidoglycan for Pseudomurien
- -Typically no outer membrane
- -Cell walls of some Archaea lack pseudomurein
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Pseudomurein
- – Polysaccharide similar to peptidoglycan
- – Composed of N-acetylglucosamine and N-acetyltalosaminuronic acid (NAG and NATAU)
- – Found in cell walls of certain methanogenic Archaea
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S-Layers
- – Most common cell wall type among Archaea
- – Consist of protein or glycoprotein
- – Paracrystalline structure
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Capsules and Slime Layers
- – Polysaccharide layers
- -May be thick or thin, rigid or flexible
- – Assist in attachment to surfaces
- – Protect against phagocytosis
- – Resist desiccation
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Fimbriae
- – Filamentous protein structures
- – Enable organisms to stick to surfaces or form pellicles
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Pili
- – Filamentous protein structures
- – Typically longer than fimbriae
- – Assist in surface attachment
- – Facilitate genetic exchange between cells(conjugation)
- – Type IV pili involved in twitching motility
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Cell Inclusions
- Carbon storage polymers
- -Poly--hydroxybutyric acid (PHB)
- -Glycogen
- -Polyphosphates
- -Sulfur globules
- -Magnetosomes
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Poly- -hydroxybutyric acid (PHB):
- lipid
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Polyphosphates:
accumulations of inorganic phosphate
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Sulfur globules:
composed of elemental sulfur
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magnetosomes:
magnetic storage inclusions
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Gas Vesicles
- – Confer buoyancy in planktonic cells
- – Spindle-shaped, gas-filled structures made ofprotein
- – Gas vesicle impermeable to water
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Endospores
- – Highly differentiated cells resistant to heat, harsh chemicals, and radiation
- – “Dormant” stage of bacterial life cycle
- – Ideal for dispersal via wind, water, or animal gut
- – Only present in some gram-positive bacteria
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Endospore Structure
- -Structurally complex
- – Contains dipicolinic acid
- – Enriched in Ca2+
- – Core contains small acid-soluble proteins(SASPs)
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3 locations of spore differentiation
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Flagellum (pl. flagella):
- structure that assistsin swimming
- – Different arrangements: peritrichous, polar,lophotrichous
- – Helical in shape
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Flagellar Structure
- – Consists of several components (Figure 3.41)
- – Filament composed of flagellin
- – Move by rotation
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Flagellar Synthesis
- – Several genes are required for flagellar synthesis and motility
- – MS ring made first
- – Other proteins and hook made next
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Flagella increase or decrease rotational speed in relation to strength of the ____________
proton motive force
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Peritrichously flagellated cells
- move slowly in a straight line
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Polarly flagellated cells
- move more rapidly and typically spin around
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Gliding Motility
- – Flagella-independent motility (Figure 3.46)– Slower and smoother than swimming
- – Movement typically occurs along long axis of cell– Requires surface contact
- – Mechanisms
- • Excretion of polysaccharide slime
- • Type IV pili
- • Gliding-specific proteins
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Taxis:
directed movement in response to chemicalor physical gradients
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Chemotaxis:
- response to chemicals
- – Best studied in E. coli
- – Bacteria respond to temporal, not spatial,difference in chemical concentration
- – “Run and tumble” behavior
- – Attractants and receptors sensed by chemoreceptors
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Phototaxis:
response to light
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Aerotaxis:
response to oxygen
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Osmotaxis:
response to ionic strength
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Hydrotaxis:
response to water
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Measuring Chemotaxis
- -Measured by inserting a capillary tube containing an attractant or a repellent in amedium of motile bacteria
- -Can also be seen under a microscope
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