华中农业大学微生物学第二章

Chapter2CellBiology,2.1Overviewofthestructureofmicrobialcells2.2Procaryoticcellwall2.3Cytoplasmicmembrane2.4Cellulargeneticinformation2.5CytoplasmicmatrixRibosomeandInclusions2.6Componentsexternaltothecellwall2.7Bacterialendospores2.8Comparisonoftheprokaryoticandeukaryoticcell,ChapterOutline,Concepts,Prokaryotesaresmallandsimpleinstructurewhencomparedwitheukaryotes,yettheyoftenhavecharacteristicshapeandsize.Prokaryoticgeneticmaterialislocatedinanareacalledthenucleoidandisnotenclosedbyamembrane.Theprokaryoticcellwallalmostalwayshaspeptidoglycanandischemicallyandmorphologicallycomplex.,Aprocaryoticcell,Aeucaryoticcell,2.1OverviewofCellStructure,3.Theircellwallalmostalwayscontainthecomplexpolysaccharidepeptidoglycan,TheProkaryoticCell,1.Theirgeneticmaterial(DNA)isnotenclosedwithinamembraneandtheylackothermembraneboundedorganelles,2.TheirDNAisnotassociatedwithhistidine,4.Theyareverysmall!,Schematicdiagramofabacterialcell,Size:Mostbacteriafallwithinarangefrom0.2to2.0umindiameterandfrom2to8uminlength,Arod-shapedprokaryoteistypicallyabout1-5micrometers(m)longandabout1mwide,Microorganismsingeneralareverysmallandarecompletelyinvisibletothenakedeye.,Acyanobacterium8x50um,sizecomparisonofmicroorganisms,Visibilityscale,Meters,RelativesizeofMicrobes,Prokaryotes,Eukaryotes,Viruses,Nakedeye,Lightmicroscope,Electronmicroscope,acellincreasesinsize,itssurfaceareatovolumeratiodecreases,Surfaceareaandvolumerelationshipsincells,spirallum,Shape:Bacteriahaveafewbasicshapes,sphericalcoccus,Rod-shapedbacillus,2.2ProkaryoticCellWall,CellWall,Thecellwallofthebacterialcellisacomplex,semi-rigidstructurethatisresponsibleforthecharacteristicshapeofthecell.Thecellwallsurroundstheunderlying,fragileplasma(cytoplasmic)membraneandprotectsitandinternalpartsofthecellfromadversechangesinthesurroundingenvironment.Almostallprokaryoteshavecellwalls.,Gram+,Gram-,Schematicdiagramofbacterialcellwalls,Bacteriacanbedividedintotwomajorgroups,calledgram-positiveandgram-negative.Theoriginaldistinctionbetweengram-positiveandgram-negativewasbasedonaspecialstainingprocedure,theGramstain,TheGram-positivecellwallhasapeptidoglycanlayerthatisrelativelythick(ca.40nm)andcomprisesapproximately90%ofthecellwall.ThecellwallsofmostGram-positiveeubacteriaalsohaveteichoicacids.,Gram-positiveCellWall,StructureoftheRepeatingUnitinPeptidoglycan,Theseconstituentsareconnectedtoformarepeatingstructure,theglycantetrapeptide.,Peptidoglycaniscomposedoftwosugarderivatives,N-acetylglucosamine(NAG)andN-acetylmuramicacid(NAM),andasmallgroupofaminoacidsconsistingofL-alanine,D-alanine,D-glutamicacid,andeitherlysineordiaminopimelicacid(DAP).,Peptideandglycanunitsareconnectedinformationofthepeptidoglycansheet,Gram-positiveBacteriafrequentlyhaveacidicpolysaccharidescalledteichoicacidsattachedtotheircellwall.Thetermteichoicacidsincludesallwall,membrane,orcapsularpolymerscontainingglycerophosphateorribitolphosphateresidues.ThesepolyalcoholsareconnectedbyphosphateestersandusuallyhaveothersugarsandD-alanineattached.,TeichoicAcids,Teichoicacidsandlipoteichoicacidsarearrangedintheoverallwallstructureofgram-positiveBacteria.,Teichoicacid,Lipoteichoicacid,TheGram-negativecellwallisathinlayerattachedtoanoutermembranevialipoproteins.Theoutermembranecontainsphospholipidonitsinnersurfaceandlipopolysaccharide(LPS)onitsoutersurface.Thespacebetweentheoutermembraneandthecytoplasmicmembraneiscalledtheperiplasmicspace.TeichoicacidsdonotoccurinGram-negativebacterialcellwalls.,Osidechain,Corepolysaccharide,LipidA,ChemicalStructureofLipopolysaccharide,MolecularModelofE.coliLipopolysaccharide,Thebondsbetweenthecarbohydratesinpseudopeptidoglycanare1-3insteadof1-4asinpeptidoglycan.,CellWallsofArchaebacteria,Thearchaebacteriadonotcontainpeptidoglycanintheircellwallsasoccursineubacteria.,N-acetylmuramicacidandD-aminoacidsarenotfoundinthecellwallsofarchaebacteria.,(Differencesfromeubacteria),Somearchaebacteriahavewallscomposedofpseudopeptidoglycan,whichresemblesthepeptidoglycanofeubacteriabutcontainsN-acetyltalosaminuronicacidinsteadofN-acetylmuramicacidandL.-aminoacidsinsteadoftheD-aminoacidsineubacterialcellwalls.,ProtoplastFormation,Peptidoglycancanbedestroyedbycertainagentsforinstancelysozyme,thatbreaksthe1,4-glycosidicbondsbetweenN-acetylglucosamineandN-acetylmuramicacidinthemolecule.,Thedifferencebetweengram-positiveandgram-negativebacteriaisduetothephysicalnatureoftheircellwalls.Ifthecellwallisremovedfromgram-positivebacteria,theybecomegramnegative.,Thepeptidoglycanseemstoactasapermeabilitybarrierpreventinglossofcrystalviolet.Gram-negativepeptidoglycanisverythin,notashighlycross-linked,andhaslargerpores.Alcoholtreatmentalsomayextractenoughlipidfromthegramnegativewalltofurtherincreaseitsporosity.Forthesereasons,alcoholmorereadilyremovesthepurplecrystalviolet-iodinecomplexfromgram-negativebacteria.,TheMechanismofGramStaining,ProceduresofGramStaining,GrampositiveorGramnegative?,Structureofcytoplasmicmembrane,2.3CytoplasmicMembrane,Functionofcytoplasmicmembrane,Membrane,B.Colorizedelectronmicrographofthecytoplasmicmembrane(CM)ofthebacteriumBacillussubtilisrevealsthecharacteristicrailroadtrackappearanceofthislipidbilayer.,StructureofCytoplasmicMembrane,ItisatypicalUNITMEMBRANE!,A.Thetypicalcytoplasmicmembraneofprokaryoticandeukaryoticcellsisalipidbilayer,asillustratedhereshowingtheorientationsofthehydrophilic(tanspheres)andhydrophobic(black)endsofphospholipidsthatmakeupthisstructure.,Thecytoplasmicmembrane,ahighlyselectivebarrier,isconstructedprincipallyoflipid,withinwhichcertainproteinsareembedded.,Membranescontainbothlipidsandproteins,althoughtheexactproportionsoflipidandproteinvarywidely.,Diagramofthestructureofcytoplasmicmembrane,3.Energyconservation-siteofgenerationanduseoftheprotonmotiveforce.,FunctionofMembrane,1.Permeabilitybarrier-preventsleakageandfunctionasgatewayfortransportofnutrientsintoandoutofthecell.,2.Proteinanchor-siteofmanyproteinsinvolvedintransport,bioenergetics,andchemotaxis.,Comparativepermeabilityofmembranemoleculestovarious,IntracellularMembraneSystem,Bacteriacellsdontcontainmembrane-enclosedorganelles.However,bacteriamayhavespecializedinvaginationsofthecytoplasmicmembrane.Theirfunctionmaybetoprovidealargermembranesurfaceforgreatermetabolicactivity.,StructureofMesosome,Mesosomemaybeinvolvedinwallformationduringdivisionorplayaroleinchromosomereplicationanddistributiontodaughtercells.Itmayalsobeinvolvedinsecretoryprocesses,2.4CellularGeneticInformation,Nucleoid,BacterialChromosomeSupercoilingandchromosomestructureChromosomalcopynumber2.Plasmids,Micrographofabacteriumshowingthenucleoidregion(green)withinthecytoplasmwherethebacterialchromosomeoccurs,ThebacterialchromosomeisacircularDNAmacromoleculeexceptinStreptomyceswhereitislinearandRhodobactersphaffoides,whichhastwoseparatechromosomes.,BacterialChromosome,Thebacterialchromosomeisusuallyasinglecovalentlyclosedcircularmolecule.,ThetermnucleoidisusedtodescribeaggregatedDNAintheprokaryoticcell.,Rangeofgenomesizesinvirousgroupsoforganismsandtheorganellesofeukarya,Thebacterialchromosomeandsupercoiling:,ExampleofE.colicell,Thereareover50supercoileddomainintheE.colichromosome.ThetotalamountofDNAisabout4600kb.IfthetotalDNAisopenedandlinearized,itwouldbe1mminlength.Thethecellisonlyabout2-3umlong.SotopackagethismuchDNAintothecellrequiresthattheDNAbehighlysupercoiled.,ElectronmicrographofanisolatednucleoidreleasedfromE.coli.,Chromosomecopynumber,Bacteriathatreproduceasexuallyaretypicallyhaploidingeneticcomplement.Rapidlygrowingcellscontainmorethan1copyofthechromosome,andonlywhencellgrowthhasceaseddoesthechromosomenumberapproachonepercell.,Reproductionofabacterialcellrequiresthereplicationofthebacterialchromosome.ThemicrographshowsthesequenceofsynthesisofnewcircularloopsofdoublehelicalDNA.,Bacterianormallyreproducebybinaryfission.Theinwardgrowthoftheseptumdividestheparentcelltoproducetwoequal-sizedprogenycells.,Plasmidsdontcontainthegeneticinformationfortheessentialmetabolicactivitiesofthecell,buttheygenerallydocontaingeneticinformationforspecialfeatures.,Plasmid,Prokaryoticcellshavesmallextra-chromosomalgeneticelementscalledplasmids.,ResistantplasmidsColplasmidsConjugativeplasmidsMetabolicplasmids,MajorTypesofPlasmids,2.5CytoplasmicMatrixRibosomeandInclusions,RibosomeCarbonstoragepolymersPHBandglycogenPhosphatepolymersSulfurGranulesGasVacuoles,Alleucaryoticandprocaryoticcellscontainribosomes,whichfunctionasthesitesofproteinsynthesis.RibosomesarecomposedoftwosubunitsProcaryoticribosomesarecalled70Sribosomes,andthoseofeucaryoticcellsareknownas80Sribosomes,Ribosomes,TheletterSreferstoSvedbergunits,whichindicatetherelativerateofsedimentationduringultra-high-speedcentrifugation,Withinthecytoplasmofprocaryotic(andeucaryotic)cellsareseveralkindsofreservedeposits,knownasinclusions.Someinclusionsarecommontoawidevarietyofbacteria,whereasothersarelimitedtoasmallnumberofspeciesandthereforeserveasabasisforidentification.Amongthemoreprominentbacterialinclusionsarethefollowing:,Inclusion,CarbonstoragepolymersPHBandglycogen,Phosphatepolymers,SulfurGranules,GasVacuoles,Polyhydroxybutyricacid(PHB),PHBisalipidlikecompound-oneofthemostcommoninclusionbodiesinprokaryoticorganisms.PHBiscommonlyfoundasastoragematerialanduniquetobacteriaGlycogenisastarchlikepolymerofglucosesubunits.GlycogengranulesareusuallysmallerthanPHBgranules.,AVibriospecies,Manymicroorganismsaccumulategranulesofpolyphosphate,whicharelargereservesofinorganicphosphatesthatcanbeusedinthesynthesisofATP,Polyphosphategranuleinabacterialcell,APseudomonasspecies,Thesulfurglobulesinsidethecellsofpurplesulfurbacterium,Chromatiumbuderi,Somebacteria,includingmanyphotosyntheticbacteria,accumulateelementalsulfurgranulesasaresultoftheirmetabolism.,Gasvacuoles(blue)andstoragegranules(red)inthecyanobacteriumMicrocystis,Theformationofgasvacuolesbyaquaticbacteriaprovidesamechanismforadjustingthebuoyancyofthecell.Manyaquaticcyanobacteriausetheirgasvacuolestomoveupanddowninthewatercolumn.,2.6Componentsexternaltothecellwall,FlagellaFimbriaeandpiliCapsulesandslimelayers,Motilityallowsthecelltoreachdifferentregionsofitsenvironment.Inthestruggleforsurvival,movementtoanewlocationmaymeanthedifferencebetweensurvivalanddeathofthecell.But,asinanyphysicalprocess,cellmovementiscloselytiedtoanenergyexpenditure,andthemovementofflagellaisnoexception.,Manyprokaryotesaremotile,andthisabilitytomoveindependentlyisusuallyduetoaspecialstructure,theflagellum(plural,flagella).,Fourbasictypesofflagellararrangements,a.monotrichous,b.amphitrichous,c.lophotrichous,d.peritrichous,Flagellaarearrangeddifferentlyondifferentbacteria.Inpolarflagellationtheflagellaareattachedatoneorbothendsofthecell.Occasionallyatuft(group)offlagellamayariseatoneendofthecell,anarrangementcalledlophotrichous.Inperitrichousflagellationtheflagellaareinsertedatmanyplacesaroundthecellsurface(perimeansaround).Thetypeofflagellation,polarorperitrichous,isoftenusedasacharacteristicintheclassificationofbacteria.,TheflagellumofaGram-negativebacterium,Thefilamentofbacterialflagellaiscomposedofsubunitsofaproteincalledflagellin.,Thebaseoftheflagellumisdifferentinstructurefromthatofthefilament.Thereisawiderregionatthebaseoftheflagellumcalledthehook.Thehookconsistsofasingletypeofproteinandfunctionstoconnectthefilamenttothemotorportionoftheflagellum.,Thebasalbodyisanchoredinthecytoplasmicmembraneandcellwall.Thebasalbodyconsistsofasmallcentralrodthatpassesthroughasystemofrings.,Ingram-positiveBacteria,whichlacktheouterlipopolysaccharidelayer,onlytheinnerpairofringsispresent.SurroundingtheinnerringandanchoredinthecytoplasmicmembraneareapairofproteinscalledMot.Theseproteinsactuallydrivetheflagellarmotorcausingatorquethatrotatesthefilament.Afinalsetofproteins,calledtheFliproteinsfunctionasthemotorswitch,reversingrotationoftheflagellainresponsetointracellularsignals.,Ingram-negativeBacteria,anouterringisanchoredinthelipopolysaccharidelayerandanotherinthepeptidoglycanlayerofthecellwall,andaninnerringislocatedwithinthecytoplasmicmembrane.,Themovementofaprocaryoticflagellumresultsfromrotationofitsbasalbodyandissimilartothemovementoftheshaftofanelectricmotor.Bacterialcellscanalterthespeedanddirectionofrotationofflagellaandthusarecapableofvariouspatternsofmotility.,Fimbriaecanbeevenlydistributedovertheentiresurfaceofthecell.Theycannumberanywherefromafewtoseveralhundredpercell.Fimbriaeallowacelltoadheretosurfacesincludingthesurfacesofothercells.,Piliareusuallylongerthanfimbriaeandnumberonlyoneortwopercell.PilifunctiontojoinbacterialcellspriortothetransferofDNAfromonecelltoanother.,Fpilus,Manyprokaryotescontainacellsurfacelayercomposedofatwo-dimensionalarrayofprotein.TheselayersarecalledS-layers.S-layershavebeendetectedinrepresentativesofvirtuallyeveryphylogeneticgroupingofBacteriaandarenearlyuniversalamongArchaea.InsomespeciesofArchaeatheS-layerisalsothecellwall.,ParacrystallineSurfaceLayers(S-Layers),ThemajorfunctionofS-layersisunknown.Astheinterfacebetweenthecellanditsenvironment,itislikelythatincellsthatproducethemtheS-layeratleastfunctionsasanexternalpermeabilitybarrier,allowingthepassageoflow-molecular-weightsubstanceswhileexcludinglargemolecules.,2.7BacterialEndospores,Certainspeciesofbacteriaproducespecialstructurecalledendospores.Theyareveryresistanttoheatandcannotbedestroyedeasily,evenbyharshchemicals.Endosporesarealsoresistanttootherharmfulagentssuchasdrying,UVradiation,acidsandchemicaldisinfectants.,Sporulatingcell,Centralcore,Cortex,Sporecoat/membrane,exosporium,Micrographofaendospore,Vegetativecell,Manyprokaryoticorganismssecreteontheirsurfacesslimyorgummymaterials.Avarietyofthesestructuresconsistofpolysaccharide,andafewconsistofprotein.Thetermscapsuleandslimelayerarefrequentlyusedtodescribepolysaccharidelayers.,Demonstrationofthepresenceofacapsuleisusuallybymeansofnegativestaining,CapsulesandSlimeLayers,LowpHvalue,andcontainssmallacid-solublesporeproteins(SASPs),StructureofDPA,PropertiesofEndosporeandItsResistance,ContainingabundantDPA(dipicolinicacid)whichiscombinedwithcalciumions.,Lowerwatercontentonly10-30%ofthewatercontentofthevegetativecell.,Sporulationinvolvesaverycomplexseriesofeventsincellulardifferentiation.Bacterialsporulationdoesnotoccurwhencellsaredividingexponentiallybutonlywhengrowthceasesowingtotheexhaustionofanessentialnutrient.Thus,cellsofBacillusceasevegetativegrowthandbeginsporulationwhenakeynutrientsuchasthecarbonornitrogensourcebecomeslimiting.,EndosporeFormatiom,Stagesinendosporeformation,1.Axialfilamentformation,2.Septumformatiom,3.Engulfmentofforespore,4.Cortexformation,5.Coatsynthesis,6.Completionofcoatsynthesis,Increaseinrefractilityandheatresistance,7.Lysisofsporangium,sporeliberation,1.ActivationUsuallyresultsfromtreatmentslikeheating.2.GerminationBreakssporesdormantstate.Thisprocessischaracterizedbysporeswelling,lossofresistancetoheatandotherstresses,lossofrefractilityandincreaseinmetabolicactivity.3.OutgrowthThesporeprotoplastmakesnewcomponentsanddevelopsoncemoreintoanactivebacterium.,SporeGermination,SeveralBacillusspecies,mostnotablyB.popilliaeandB.thuringiensis,produceintracellularcrystalsoftoxicglycoproteinswhentheysporulate.,Toxiccrystals,ParasporalCrystal,(Spore-companionedcrystal),2.8ComparisonofTheProkaryoticandEucaryoticCell,TheirDNAisassociatedwithhistoneproteins.,membrane-boundedorganelles,9+2typeflagella,EucaryoticCell,Thechiefdistinguishingcharacteristicsofprocaryoticcellsare:1.Theirgeneticmaterial(DNA)isnotenclosedwithinamembrane.2.Theylackothermembrane-boundedorganelles.3.TheirDNAisnotassociatedwithhistoneproteins.4.Theircellwallsalmostalwayscontainthecomplexpolysaccharidepeptidoglycan.5.Theyusuallydividebybinaryfission.Duringthisprocess,theDNAiscopiedandthecellsplitsintotwocells.,Summary1.Prokaryoticgeneticmaterialislocatedinanareacalledthenucleoidandisnotenclosedbyamembrane.2.Mostbacteriahaveacellwalloutsidetheplasmamembranetogivethemshapeandprotectthemfromosmoticlysis.Bacterialwallsarechemicallycomplexandusuallycontainpeptidoglycanormurein.,3.BacteriaoftenareclassfiedaseithergrampositiveorgramnegativebasedondifferencesincellwallstructureandtheirresponsetoGramstaining.Gram-positivewallshavethick,homogeneouslayersofpeptidoglycanandteichoidacid.Gram-negativebacteriahaveathinpeptidoglycanlayers