Dr. Alvin Fox

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The external layers of vegetative cells and
spores
Dr. Alvin Fox
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KEY WORDS
Cell envelope Teichoic acid Cell
wall Teichuronic acid Cell membrane Lipoteic
hoic acid Outer membrane Mycolic
acid Peptidoglycan Undecaprenol
(bactoprenol) Braun lipoprotein Endospore
(spore) Porins Cell
division Lipopolysaccharide
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Topics

• Structure of vegetative cell envelopes
• unique cell envelope molecules
• biosynthesis of cell wall constituents
• Endospores (dormant cells)
• Cell division

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Cell Envelope

• Cell membrane cell wall ( plus outer
  membrane)
• Cell wall
• peptidoglycan
• attached structures.

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Bacterial cell envelopes
Gram stain ( or -) correlates with structure
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Gram positive
Gram negative
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Peptidoglycan

• single macromolecule
• highly cross-linked
• surrounds cell
• provides rigidity

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Peptidoglycan

• glycan backbone
• muramic acid
• glucosamine
• peptide side chain
• peptide cross-bridge
• D- and L- amino acids
• diaminopimelic acid

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• Muramic acid, D-amino acids diaminopimelic acid
• not synthesized by mammals

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Peptidoglycan
L-alanine D-glutamic acid L-lysine/Diaminopimelic
acid D-alanine D-alanine
Muramic acid
Glucosamine
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Gram Positive Cell Envelope

• Teichoic acid
• polymer
• ribitol phosphate or ribitol glycerol backbone
• Teichuronic acid
• polymer
• no phosphorus
• glucuronic acid

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Teichoic and teichuronic acids

• Metal ion uptake
• Direct autolytic enzymes
• holes punched in cell wall
• allows insertion cell wall (synthesis)

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Lipoteichoic acids

• cell membrane
• autolysins kept from cell wall

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Gram Positive Cell Envelope
Lipoteichoic acid
Peptidoglycan-teichoic acid
Cytoplasmic membrane
Cytoplasm
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Gram Negative Peptidoglycan

• Braun lipoprotein
• binds cell wall to outer membrane

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Outer Membrane

• lipopolysaccharide
• phospholipids
• Proteins
• porins

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Lipopolysaccharide
O-antigen Highly variable
n

• Core
• Heptoses
• Ketodeoxyoctonic acid

• Lipid A
• Glucosamine disaccharide
• Beta hydroxy fatty acids

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Gram Negative Cell Envelope
Lipopolysaccharide
Porin
Outer Membrane
Braun lipoprotein
Peptidoglycan
Cytoplasm
Inner (cytoplasmic) membrane
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Acid Fast Cell Envelope
Mycolic acid lipids
Peptidoglycan-mycolic acid-arabinogalactan
Cytoplasmic membrane
Cytoplasm
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Peptidoglycan synthesis
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Cell Membrane
Cytoplasm
Cell wall
undecaprenol
sugar
amino acid
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Lipopolysaccharide

• synthesis similar to peptidoglycan
• also on undecaprenol carrier

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Spore

• Modified Gram positive bacteria cell
• unusual cell envelope
• cell membrane
• outer membrane

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Spore

• Peptidoglycan layer
• cortex
• between two membranes
• less cross-linked
• dehydrated muramic acid (lactam)

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Vegetative cell division
Sporulation
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The endospore
exosporium
coat
outer membrane
Inner membrane
cortex
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