华中农业大学微生物学第二章

Chapter2

CellBiology第一页，共九十二页。

2.1Overviewofthestructureofmicrobialcells2.2Procaryoticcellwall2.3Cytoplasmicmembrane2.4Cellulargeneticinformation2.5Cytoplasmicmatrix–RibosomeandInclusions2.6Componentsexternaltothecellwall2.7Bacterialendospores2.8ComparisonoftheprokaryoticandeukaryoticcellChapterOutline第二页，共九十二页。ConceptsProkaryotesaresmallandsimpleinstructurewhencomparedwitheukaryotes,yettheyoftenhavecharacteristicshapeandsize.

Prokaryoticgeneticmaterialislocatedinanareacalledthenucleoidandisnotenclosedbyamembrane.Theprokaryoticcellwallalmostalwayshaspeptidoglycanandischemicallyandmorphologicallycomplex.第三页，共九十二页。AprocaryoticcellAeucaryoticcell2.1OverviewofCellStructure第四页，共九十二页。3.TheircellwallalmostalwayscontainthecomplexpolysaccharidepeptidoglycanTheProkaryoticCell1.Theirgeneticmaterial(DNA)isnotenclosedwithinamembraneandtheylackothermembrane–boundedorganelles2.TheirDNAisnotassociatedwithhistidine4.Theyareverysmall!!第五页，共九十二页。Schematicdiagramofabacterialcell第六页，共九十二页。Size:

Mostbacteriafallwithinarangefrom0.2to2.0umindiameterandfrom2to8uminlengthArod-shapedprokaryoteistypicallyabout1-5micrometers(μm)longandabout1μmwideMicroorganismsingeneralareverysmallandarecompletelyinvisibletothenakedeye.

Acyanobacterium8x50um第七页，共九十二页。sizecomparisonofmicroorganismsVisibility

scaleMeters

RelativesizeofMicrobesProkaryotesEukaryotesVirusesNakedeyeLightmicroscopeElectronmicroscope第八页，共九十二页。acellincreasesinsize,itssurfacearea–to–volumeratiodecreasesSurfaceareaandvolumerelationshipsincells第九页，共九十二页。spirallumShape:

Bacteriahaveafewbasicshapesspherical

coccusRod-shaped

bacillus第十页，共九十二页。2.2ProkaryoticCellWallCellWall第十一页，共九十二页。Thecellwallofthebacterialcellisacomplex,semi-rigidstructurethatisresponsibleforthecharacteristicshapeofthecell.Thecellwallsurroundstheunderlying,fragileplasma(cytoplasmic)membraneandprotectsitandinternalpartsofthecellfromadversechangesinthesurroundingenvironment.Almostallprokaryoteshavecellwalls.第十二页，共九十二页。Gram+Gram-SchematicdiagramofbacterialcellwallsBacteriacanbedividedintotwomajorgroups,calledgram-positiveandgram-negative.Theoriginaldistinctionbetweengram-positiveandgram-negativewasbasedonaspecialstainingprocedure,theGramstain第十三页，共九十二页。TheGram-positivecellwallhasapeptidoglycanlayerthatisrelativelythick(ca.40nm)andcomprisesapproximately90%ofthecellwall.ThecellwallsofmostGram-positiveeubacteriaalsohaveteichoicacids.Gram-positiveCellWall第十四页，共九十二页。StructureoftheRepeatingUnitinPeptidoglycanTheseconstituentsareconnectedtoformarepeatingstructure,theglycantetrapeptide.Peptidoglycaniscomposedoftwosugarderivatives,N-acetylglucosamine(NAG)andN-acetylmuramicacid(NAM),andasmallgroupofaminoacidsconsistingofL-alanine,D-alanine,D-glutamicacid,andeitherlysineordiaminopimelicacid(DAP).第十五页，共九十二页。第十六页，共九十二页。Peptideandglycanunitsareconnectedinformationofthepeptidoglycansheet第十七页，共九十二页。Gram-positiveBacteriafrequentlyhaveacidicpolysaccharidescalledteichoicacidsattachedtotheircellwall.Thetermteichoicacidsincludesallwall,membrane,orcapsularpolymerscontainingglycerophosphateorribitolphosphateresidues.ThesepolyalcoholsareconnectedbyphosphateestersandusuallyhaveothersugarsandD-alanineattached.

TeichoicAcids第十八页，共九十二页。Teichoicacidsandlipoteichoicacidsarearrangedintheoverallwallstructureofgram-positiveBacteria.TeichoicacidLipoteichoicacid第十九页，共九十二页。TheGram-negativecellwallisathinlayerattachedtoanoutermembranevialipoproteins.Theoutermembranecontains

phospholipidonitsinnersurfaceand

lipopolysaccharide(LPS)

on

itsoutersurface.Thespacebetweentheoutermembraneandthe

cytoplasmicmembraneiscalledthe

periplasmicspace.Teichoic

acidsdonotoccurinGram-negativebacterialcellwalls..

第二十页，共九十二页。第二十一页，共九十二页。OsidechainCorepolysaccharideLipidAChemicalStructureofLipopolysaccharide第二十二页，共九十二页。MolecularModelofE.coliLipopolysaccharide第二十三页，共九十二页。Thebondsbetweenthecarbohydratesinpseudopeptidoglycanare

β1-3insteadof'β1-4

asinpeptidoglycan.

CellWallsofArchaebacteriaThearchaebacteria

donotcontainpeptidoglycan

intheircellwallsasoccursineubacteria.N-acetylmuramicacidandD-aminoacids

arenotfound

inthecellwallsofarchaebacteria.(Differencesfromeubacteria)第二十四页，共九十二页。Somearchaebacteriahavewallscomposedof

pseudopeptidoglycan,

whichresemblesthepeptidoglycanofeubacteriabut

containsN-acetyltalosaminuronicacid

insteadofN-acetylmuramicacidand

L.-aminoacids

insteadoftheD-aminoacidsineubacterialcellwalls.第二十五页，共九十二页。ProtoplastFormation

Peptidoglycancanbedestroyedbycertainagentsforinstancelysozyme,thatbreaksthe1,4-glycosidicbondsbetweenN-acetylglucosamineandN-acetylmuramicacidinthemolecule.第二十六页，共九十二页。Thedifferencebetweengram-positiveandgram-negativebacteriaisduetothephysicalnatureoftheircellwalls.Ifthecellwallisremovedfromgram-positivebacteria,theybecomegramnegative.

第二十七页，共九十二页。Thepeptidoglycanseemstoactasapermeabilitybarrierpreventinglossofcrystalviolet.Gram-negativepeptidoglycanisverythin,notashighlycross-linked,andhaslargerpores.Alcoholtreatmentalsomayextractenoughlipidfromthegramnegativewalltofurtherincreaseitsporosity.Forthesereasons,alcoholmorereadilyremovesthepurplecrystalviolet-iodinecomplexfromgram-negativebacteria.TheMechanismofGramStaining第二十八页，共九十二页。

ProceduresofGramStaining第二十九页，共九十二页。GrampositiveorGramnegative?第三十页，共九十二页。第三十一页，共九十二页。Structureofcytoplasmicmembrane2.3CytoplasmicMembraneFunctionofcytoplasmicmembraneMembrane第三十二页，共九十二页。B.

Colorizedelectronmicrographof'thecytoplasmicmembrane(CM)ofthebacteriumBacillussubtilis

revealsthecharacteristicrailroadtrackappearanceofthislipidbilayer.

StructureofCytoplasmicMembraneItisatypicalUNITMEMBRANE!A.

Thetypicalcytoplasmicmembraneofprokaryoticandeukaryoticcellsisalipidbilayer,asillustratedhereshowingtheorientationsofthehydrophilic(tanspheres)andhydrophobic(black)endsofphospholipidsthatmakeupthisstructure.第三十三页，共九十二页。Thecytoplasmicmembrane,ahighlyselectivebarrier,isconstructedprincipallyoflipid,withinwhichcertainproteinsareembedded.Membranescontainboth

lipidsandproteins,althoughtheexactproportionsoflipidandproteinvarywidely.第三十四页，共九十二页。Diagramofthestructureofcytoplasmicmembrane第三十五页，共九十二页。3.Energyconservation-siteofgenerationanduseoftheprotonmotiveforce.

FunctionofMembrane1.Permeabilitybarrier

-preventsleakageandfunctionasgatewayfortransportofnutrientsintoandoutofthecell.2.Proteinanchor-siteofmanyproteinsinvolvedintransport,bioenergetics,andchemotaxis.第三十六页，共九十二页。

Rateofpermeability*

100

0.1

0.001

0.001

0.000001

0.0000001

0.00000001

Substance

Water

Glycerol

Tryptophan

Glucose

Chlorideion(Cl-)

Patassiumion(K+)

Sodiumion(Na+)

*Relativerate:Permeabilitywithrespecttopermeabilityofwatergivenas100

Comparativepermeabilityofmembranemoleculestovarious

第三十七页，共九十二页。IntracellularMembraneSystemBacteriacellsdon’tcontainmembrane-enclosedorganelles.However,bacteriamayhavespecializedinvaginationsofthecytoplasmicmembrane.Theirfunctionmaybetoprovidealargermembranesurfaceforgreatermetabolicactivity.第三十八页，共九十二页。StructureofMesosomeMesosomemaybeinvolvedin

wallformation

duringdivisionorplayarolein

chromosomereplication

anddistributiontodaughtercells.Itmayalsobeinvolvedin

secretoryprocesses第三十九页，共九十二页。2.4CellularGeneticInformationNucleoid第四十页，共九十二页。BacterialChromosomeSupercoilingandchromosomestructureChromosomalcopynumber2.Plasmids第四十一页，共九十二页。Micrographofabacteriumshowingthenucleoidregion(green)withinthecytoplasmwherethebacterialchromosomeoccurs第四十二页，共九十二页。ThebacterialchromosomeisacircularDNAmacromoleculeexcept

inStreptomyces

whereitislinearand

Rhodobacter

sphaffoides,whichhastwoseparatechromosomes.

BacterialChromosomeThebacterialchromosomeisusuallya

singlecovalentlyclosedcircular

molecule.Theterm

nucleoidisusedtodescribeaggregatedDNAintheprokaryoticcell.第四十三页，共九十二页。Rangeofgenomesizesinvirousgroupsoforganismsandtheorganellesofeukarya第四十四页，共九十二页。Thebacterialchromosomeandsupercoiling:第四十五页，共九十二页。ExampleofE.colicellThereareover

50supercoileddomain

intheE.colichromosome.ThetotalamountofDNAisabout

4600kb.IfthetotalDNAisopenedandlinearized,itwouldbe

1mminlength.Thethecellisonly

about2-3umlong.

SotopackagethismuchDNAintothecellrequiresthat

theDNAbehighlysupercoiled.第四十六页，共九十二页。ElectronmicrographofanisolatednucleoidreleasedfromE.coli.

第四十七页，共九十二页。Chromosomecopynumber

Bacteriathatreproduceasexuallyaretypically

haploid

ingeneticcomplement.Rapidlygrowingcellscontain

morethan

1copy

ofthechromosome,andonlywhencellgrowthhasceaseddoesthechromosomenumberapproachonepercell.第四十八页，共九十二页。

Reproductionofabacterialcellrequiresthereplicationofthebacterialchromosome.ThemicrographshowsthesequenceofsynthesisofnewcircularloopsofdoublehelicalDNA.Bacterianormallyreproducebybinaryfission.Theinwardgrowthoftheseptumdividestheparentcelltoproducetwoequal-sizedprogenycells.第四十九页，共九十二页。Plasmidsdon’tcontainthegeneticinformationfortheessentialmetabolicactivitiesofthecell,buttheygenerallydocontaingeneticinformationforspecialfeatures.

PlasmidProkaryoticcellshavesmallextra-chromosomal

geneticelementscalled

plasmids.第五十页，共九十二页。ResistantplasmidsColplasmidsConjugativeplasmidsMetabolicplasmids

MajorTypesofPlasmids第五十一页，共九十二页。2.5CytoplasmicMatrixRibosomeandInclusionsRibosomeCarbonstoragepolymers–PHBandglycogenPhosphatepolymersSulfurGranulesGasVacuoles第五十二页，共九十二页。Alleucaryoticandprocaryoticcellscontainribosomes,whichfunctionasthesitesofproteinsynthesis.Ribosomesarecomposedoftwosubunits

Procaryoticribosomesarecalled70Sribosomes,andthoseofeucaryoticcellsareknownas80Sribosomes

RibosomesTheletterSreferstoSvedbergunits,whichindicatetherelativerateofsedimentationduringultra-high-speedcentrifugation第五十三页，共九十二页。第五十四页，共九十二页。

Withinthecytoplasmofprocaryotic(andeucaryotic)cellsareseveralkindsofreservedeposits,knownasinclusions.Someinclusionsarecommontoawidevarietyofbacteria,whereasothersarelimitedtoasmallnumberofspeciesandthereforeserveasabasisforidentification.Amongthemoreprominentbacterialinclusionsarethefollowing:InclusionCarbonstoragepolymers–PHBandglycogenPhosphatepolymersSulfurGranulesGasVacuoles第五十五页，共九十二页。Polyhydroxybutyricacid(PHB)PHBisa

lipidlikecompound

-oneofthemostcommoninclusionbodiesinprokaryoticorganisms.PHBiscommonlyfoundasastoragematerialand

uniquetobacteria

Glycogenisa

starchlikepolymer

ofglucosesubunits.GlycogengranulesareusuallysmallerthanPHBgranules.AVibriospecies第五十六页，共九十二页。Manymicroorganismsaccumulategranulesofpolyphosphate,whicharelargereservesof

inorganicphosphates

thatcanbeusedinthesynthesisofATPPolyphosphategranule

inabacterialcellAPseudomonasspecies第五十七页，共九十二页。ThesulfurglobulesinsidethecellsofpurplesulfurbacteriumChromatiumbuderiSomebacteria,includingmanyphotosyntheticbacteria,accumulate

elementalsulfurgranules

asaresultoftheirmetabolism.第五十八页，共九十二页。Gasvacuoles(blue)andstoragegranules(red)inthecyanobacteriumMicrocystisTheformationofgasvacuolesbyaquaticbacteriaprovidesamechanismforadjustingthebuoyancyofthecell.Manyaquaticcyanobacteriausetheirgasvacuolestomoveupanddowninthewatercolumn.第五十九页，共九十二页。2.6ComponentsexternaltothecellwallFlagellaFimbriaeandpiliCapsulesandslimelayers第六十页，共九十二页。Motilityallowsthecelltoreachdifferentregionsofitsenvironment.Inthestruggleforsurvival,movementtoanewlocationmaymeanthedifferencebetweensurvivalanddeathofthecell.But,asinanyphysicalprocess,cellmovementiscloselytiedtoanenergyexpenditure,andthemovementofflagellaisnoexception.

Manyprokaryotesaremotile,andthisabilitytomoveindependentlyisusually

duetoaspecialstructure,

the

flagellum

(plural,flagella).

第六十一页，共九十二页。第六十二页，共九十二页。Fourbasictypesofflagellararrangementsa.monotrichousb.amphitrichousc.

lophotrichousd.peritrichous第六十三页，共九十二页。Flagellaarearrangeddifferentlyondifferentbacteria.Inpolarflagellationtheflagellaareattachedatoneorbothendsofthecell.Occasionallyatuft(group)offlagellamayariseatoneendofthecell,anarrangementcalledlophotrichous.Inperitrichousflagellationtheflagellaareinsertedatmanyplacesaroundthecellsurface(perimeans"around").Thetypeofflagellation,polarorperitrichous,isoftenusedasacharacteristicintheclassificationofbacteria.第六十四页，共九十二页。

TheflagellumofaGram-negativebacterium第六十五页，共九十二页。Thefilamentofbacterialflagellaiscomposedofsubunitsofaproteincalled

flagellin.

Thebaseoftheflagellumisdifferentinstructurefromthatofthefilament.Thereisawiderregionatthebaseoftheflagellumcalledthe

hook.Thehookconsistsofasingletypeofproteinandfunctionstoconnectthefilamenttothemotorportionoftheflagellum.

The

basalbody

isanchoredinthecytoplasmicmembraneandcellwall.Thebasalbodyconsistsofasmallcentralrodthatpassesthroughasystemofrings.第六十六页，共九十二页。Ingram-positiveBacteria,whichlacktheouterlipopolysaccharidelayer,onlytheinnerpairofringsispresent.SurroundingtheinnerringandanchoredinthecytoplasmicmembraneareapairofproteinscalledMot.Theseproteinsactuallydrivetheflagellarmotorcausingatorquethatrotatesthefilament.Afinalsetofproteins,calledtheFliproteinsfunctionasthemotorswitch,reversingrotationoftheflagellainresponsetointracellularsignals.Ingram-negativeBacteria,anouterringisanchoredinthelipopolysaccharidelayerandanotherinthepeptidoglycanlayerofthecellwall,andaninnerringislocatedwithinthecytoplasmicmembrane.第六十七页，共九十二页。Themovementofaprocaryoticflagellumresultsfromrotationofitsbasalbodyandissimilartothemovementoftheshaftofanelectricmotor.Bacterialcellscanalterthespeedanddirectionofrotationofflagellaandthusarecapableofvariouspatternsofmotility.第六十八页，共九十二页。Fimbriae

canbeevenlydistributedovertheentiresurfaceofthecell.Theycannumberanywherefromafewtoseveralhundredpercell.Fimbriaeallowacelltoadheretosurfacesincludingthesurfacesofothercells.

Piliareusuallylongerthanfimbriaeandnumberonlyoneortwopercell.PilifunctiontojoinbacterialcellspriortothetransferofDNAfromonecelltoanother.Fpilus第六十九页，共九十二页。Manyprokaryotescontainacellsurfacelayercomposedofatwo-dimensionalarrayofprotein.TheselayersarecalledS-layers.S-layershavebeendetectedinrepresentativesofvirtuallyeveryphylogeneticgroupingofBacteriaandarenearlyuniversalamongArchaea.InsomespeciesofArchaeatheS-layerisalsothecellwall.ParacrystallineSurfaceLayers(S-Layers)第七十页，共九十二页。ThemajorfunctionofS-layersisunknown.Astheinterfacebetweenthecellanditsenvironment,itislikelythatincellsthatproducethemtheS-layeratleastfunctionsasanexternalpermeabilitybarrier,allowingthepassageoflow-molecular-weightsubstanceswhileexcludinglargemolecules.第七十一页，共九十二页。2.7BacterialEndosporesCertainspeciesofbacteriaproducespecialstructurecalledendospores.Theyareveryresistanttoheatandcannotbedestroyedeasily,evenbyharshchemicals.Endosporesarealsoresistanttootherharmfulagentssuchasdrying,UVradiation,acidsandchemicaldisinfectants.第七十二页，共九十二页。SporulatingcellCentralcoreCortexSporecoat/membraneexosporiumMicrographofaendosporeVegetativecell第七十三页，共九十二页。第七十四页，共九十二页。Manyprokaryoticorganismssecreteontheirsurfacesslimyorgummymaterials.Avarietyofthesestructuresconsistofpolysaccharide,andafewconsistofprotein.Thetermscapsuleandslimelayerarefrequentlyusedtodescribepolysaccharidelayers.Demonstrationofthepresenceofacapsuleisusuallybymeansofnegativestaining

CapsulesandSlimeLayers第七十五页，共九十二页。LowpHvalue,andcontainssmallacid-solublesporeproteins(SASPs)StructureofDPA

PropertiesofEndosporeandItsResistanceContainingabundantDPA(dipicolinicacid)whichiscombinedwithcalciumions.Lowerwatercontent–only10-30%ofthewatercontentofthevegetativecell.第七十六页，共九十二页。Sporulationinvolvesaverycomplexseriesofeventsincellulardifferentiation.Bacterialsporulationdoesnotoccurwhencellsaredividingexponentiallybutonlywhengrowthceasesowingtotheexhaustionofanessentialnutrient.Thus,cellsofBacillusceasevegetativegrowthandbeginsporulationwhenakeynutrientsuchasthecarbonornitrogensourcebecomeslimiting.EndosporeFormatiom第七十七页，共九十二页。

Stagesinendosporeformation1.Axialfilamentformation2.Septumformatiom3.Engulfmentofforespore4.Cortexformation5.Coatsynthesis6.Completionofcoatsynthesis,Increaseinrefractilityandheatresistance7.Lysisofsporangium,sporeliberation第七十八页，共九十二页。第七十九页，共九十二页。1.Activation–

Usuallyresultsfromtreatmentslikeheating.2.Germination–

Breaksspore’sdormantstate.Thisprocessischaracterizedbysporeswelling,lossofresistancetoheatandotherstresses,lossofrefractilityandincreaseinmetabolicactivity.3.Outgrowth–

Thesporeprotoplastmakesnewcomponentsanddevelopsoncemoreintoanactivebacterium.SporeGermination第八十页，共九十二页。SeveralBacillusspecies,mostnotablyB.popilliaeandB.thuringiensis,produceintracellularcrystalsoftoxicglycoproteinswhentheysporulate.ToxiccrystalsParasporalCrystal(Spore-companionedcrystal)第八十一页，共九十二页。2.8ComparisonofTheProkaryoticandEucaryoticCellPropertiesProkaryoteEukaryotePhylogeneticgroupsBacteria,ArchaeaEukarya:Algae,fungi,protozoa,plants,animalsSizeGenerallysmall,usually<2µmindiameterUsuallylarge,2to100µmindiameterNuclearmembranesAbsentPresentNucleolusAbsentPresentDNANotmitosisMitosis;mitoticapparatuswithmicrotubularspindle第八十二页，共九十二页。PropertiesProkaryoteEukaryoteCytoplasmicmembraneUsuallylackssterols;hopanoidsmaybepresentSterolsusuallypresent;hopanoidsabsentRibosomes70sinsize80s,exceptforribosomesofmitochondriaandchloroplastswhichare70sMembranousorganellesAbsentSeveralpresentRespirationsystemPartofcytoplasmicmembrane;mitochondriaabsentInmitochondria;hydrogenosomesincertainanaerobicspeciesCellwallsPresent(inmost),composedofpeptidoglycan(bacteria),protein,otherpolysaccharides,glycoprotein(Archaea)Presentinplants,algae,fungi,usuallypolysaccharide;absentinanimals,mostprotozoa第八十三页，共九十二页。TheirDNAisassociatedwithhistoneproteins.membrane-boundedorganelles9+2typeflagellaEucaryoticCell第八十四页，共九十二页。Thechiefdistinguishingcharacteristicsofprocaryoticcellsare:1.Theirgeneticmaterial(DNA)isnotenclosedwithinamembrane.2.Theylackothermembrane-boundedorganelles.3.TheirDNAisnotassociatedwithhistoneproteins.4.Theircellwallsalmostalwayscontainthecomplexpolysaccharidepeptidoglycan.5. Theyusuallydividebybinaryfission.Duringthisprocess,theDNAiscopiedandthecellsplitsintotwocells.

第八十五页，共九十二页。Summary1.Prokaryoticgeneticmaterialislocatedinanareacalledthenucleoidandisnotenclosedbyamembrane.2.Mostbacteriahaveacellwalloutsidetheplasmamembranetogivethemshapeandprotectthemfromosmoticlysis.Bacterialwallsarechemicallycomplexandusuallycontain

peptidoglycanormurein.第八十六页，共九十二页。3.Bacteriaoftenareclassfiedaseithergrampositiveorgramnegativebasedondifferencesincellwallstructureandtheirresponseto

Gramstain