Medical Microbiology

152 3 GeneralBacteriology

proteinsarepermeases,enzymesforthebiosynthesisofthecellwall,transfer

proteinsforsecretionofextracellularproteins,sensororsignalproteins,and

respiratorychainenzymes.

InelectronmicroscopicimagesofGram-positivebacteria,themesosomes

appearasstructuresboundtothemembrane.Howtheyfunctionandwhat

roletheyplayremaintobeclarified.Theymaybenomorethanartifacts.

CellWall...............................................

Thetasksofthecomplexbacterialcellwallaretoprotecttheprotoplastsfrom

externalnoxae,towithstandandmaintaintheosmoticpressuregradientbe-

tweenthecellinteriorandtheextracellularenvironment(withinternalpres-

suresashighas 500 – 2000 kPa),togivethecellitsouterformandtofacilitate

communicationwithitssurroundings.

Murein(syn.peptidoglycan).Themostimportantstructuralelementof

thewallismurein,anetlikepolymermaterialsurroundingtheentirecell

(sacculus).Itismadeupofpolysaccharidechainscrosslinkedbypeptides

(Figs.3. 8 and3. 9 ).

ThecellwallofGram-positivebacteria(Fig.3. 10 ).Themureinsacculusmay

consistofasmanyas 40 layers(1 5 – 80 nmthick)andaccountforasmuchas

BasicBacterialCellStructure

Nucleus

equivalent

(syn. nucleoid)

Cell wall

murein

Capsule

Plasmid

Cytoplasmic

membrane 70S ribosomes

Depot substances

• metaphosphates (volutin)


• glycogen (granulose)

Attachment

pili

Flagella

Outer

membrane

(only in

gram-

negative

bacteria)

Fig.3. 7 Allbacteriahavethesamebasicstructure(nottoscale).

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Kayser, Medical Microbiology © 2005 Thieme