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Dr. Alvin Fox

The external layers of vegetative cells and spores

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KEY WORDSKEY WORDS

Cell envelope Teichoic acid

Cell wall Teichuronic acid

Cell membrane Lipoteichoic acid

Outer membrane Mycolic acid

Peptidoglycan Undecaprenol (bactoprenol)

Braun lipoprotein Endospore (spore)

Porins Cell division

Lipopolysaccharide

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Topics:Topics:

• Structure of vegetative cell envelopesStructure of vegetative cell envelopes

– unique cell envelope molecules unique cell envelope molecules

– biosynthesisbiosynthesis of cell wall constituents of cell wall constituents

• Endospores (dormant cells)Endospores (dormant cells)

• Cell division Cell division

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Cell EnvelopeCell Envelope

• Cell membrane + cell wall (+ plus outer ell membrane + cell wall (+ plus outer membrane)membrane)

• Cell wallCell wall

– peptidoglycan peptidoglycan

– attached structuresattached structures.

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Bacterial cell envelopes Bacterial cell envelopes

Gram stain (+ or -) correlates with structureGram stain (+ or -) correlates with structure

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Gram positiveGram positive

Gram negativeGram negative

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PeptidoglycanPeptidoglycan

• single macromolecule single macromolecule

• highly cross-linkedhighly cross-linked

• surrounds cellsurrounds cell

• provides rigidityprovides rigidity

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PeptidoglycanPeptidoglycan

• 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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PeptidoglycanPeptidoglycan

Muramic acid

Glucosamine

L-alanineD-glutamic acidL-lysine/Diaminopimelic acidD-alanineD-alanine

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Gram Positive Cell EnvelopeGram 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 acidsTeichoic and teichuronic acids

• Metal ion uptake

• Direct autolytic enzymes– holes punched in cell wall holes punched in cell wall

– allows insertion cell wall (synthesis) allows insertion cell wall (synthesis)

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Lipoteichoic acids

• cell membrane

• autolysins kept from cell wall

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r r rrr

r

Gram Positive Cell EnvelopeGram Positive Cell Envelope

CytoplasmCytoplasm

rrrr

Lipoteichoic acid

Peptidoglycan-teichoic acid

Cytoplasmic membrane

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• Braun lipoproteinBraun lipoprotein

– binds cell wall to outer membrane binds cell wall to outer membrane

Gram Negative PeptidoglycanGram Negative Peptidoglycan

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Outer MembraneOuter Membrane

• lipopolysaccharidelipopolysaccharide

• phospholipidsphospholipids

• ProteinsProteins

– porinsporins

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Lipopolysaccharide

Lipid A• Glucosamine disaccharide

• Beta hydroxy fatty acids

Core • Heptoses• Ketodeoxyoctonic acid

O-antigenHighly variablen

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CytoplasmCytoplasm

Inner (cytoplasmic) membrane

Ou

ter

Mem

bra

ne Lipopolysaccharide

Porin

Braun lipoprotein

Gram Negative Cell EnvelopeGram Negative Cell Envelope

Peptidoglycan

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r r rrr

r

Acid Fast Cell EnvelopeAcid Fast Cell Envelope

CytoplasmCytoplasm

rrrr

Peptidoglycan-mycolic acid-arabinogalactan

Cytoplasmic membrane

Mycolic acid lipids

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Peptidoglycan synthesisPeptidoglycan synthesis

CytoplasmCytoplasm Cell wallCell wall

undecaprenolundecaprenol

sugarsugar

aminoaminoacidacid

Cell MembraneCell Membrane

1 2 3

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LipopolysaccharideLipopolysaccharide• synthesis similar to peptidoglycan

• also on undecaprenol carrier

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SporeSpore

• Modified Gram positive bacteria cellModified Gram positive bacteria cell

– unusual cell envelopeunusual cell envelope• cell membranecell membrane• outer membraneouter membrane

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SporeSpore

• Peptidoglycan layerPeptidoglycan layer– cortexcortex– between two membranesbetween two membranes– less cross-linkedless cross-linked– dehydrated muramic acid (lactam) dehydrated muramic acid (lactam)

24Vegetative

cell division Sporulation

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cortexcortex

The endosporeThe endospore

exosporiumexosporium

coatcoat

Inner Inner membranemembrane

outer outer membranemembrane

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