兽医微生物学双语课件

Biologyofmicroorganisms

IntroductionHowtouseyourtextbook?What’sthearrangementfortheteaching?WhyshouldwestudymicrobiologyLecture(70hours)Laboratorypractice(50hours)Mini-test(10times)Open-laboratorypracticeClubactivityArrangementWhyshouldwestudymicrobiology?Twomajorreasonsmicrobiologydealswithmanyimportantpracticalproblemsinmedicine,agriculture,andindustry.Biochemicalandgeneticstudy

AsabasicbiologicalscienceAsanappliedbiologicalscienceProvidesresearchtoolstheexperimentalbasisofmicrobiologythegeneralprinciplesofcellstructureandfunctiontheclassificationanddiversityofmicroorganismsbiochemicalprocessesincellsthegeneticbasisofmicrobialgrowthandevolutiontheecologicalactivitiesofmicroorganismsinnature.

Wewilldiscuss:

Howtouseyourtextbook?TheCHAPTEROUTLINE

providesanoverviewofthechapter’smainconcepts.

SECTIONNUMBERS

keydetopagenumbersprovideeasyreferencepoints.TheWORKINGGLOSSARY

providesdefinitionsofimportanttermswithineachchapter.(BrockBiologyofMicroorganisms,NinthEdition)CONCEPTCHECKS

summarizeeachsectionandprovidequizquestions,sostudentscanevaluatetheirunderstandingastheyprogressthroughthechapter.CONCEPTLINKS

alertstudentstomaterialthatbuildsonpreviousconceptsandprovidesausefulcross-referencingsystemfortheentirebook.OutstandingMICROGRAPHSareincludedthroughout.

TABLEShavebeenredesignedtomakekeyinformationevenmoreaccessibletostudents.TheART

inthenintheditionhasbeenthoroughlyrevised,butstillmaintainstheuseofconsistentcolorcoding.BOLDFACEDTERMS

aredefinedintheGlossary.FEATUREBOXES

provideadditional,relevantinformation.Sometakeanhistoricalperspective,somefocusontechniquesandapplications,andothersexploreatexttopicingreaterdepth.REVIEWQUESTIONS

challengethestudent’smasteryofchapterconcepts.APPLICATIONQUESTIONS

allowstudentstotesttheiranalyticalandproblem-solvingskills.APPENDICESprovideusefultutorialandreferenceinformation.BackBackBackBackBackBackBackBackAveryeffectivestudytechniquetoyou

SurveyQuestion

ReadReviseRecord

ReviewSQ4RTechniqueTocontinueSurvey

Brieflyscanthechaptertobecomefamiliarwithitsgeneralcontent.Quicklyreadthetitle,introduction,summary,andmainheadings.Recordthemajorideasandpointsthatyouthinkthechapterwillmake.Iftherearealistofchapterconceptsandachapteroutline,paycloseattentiontothese.Thissurveyshouldgiveyouafeelforthetopicandhowthechapterisapproachingit.Question

Asyoureacheachmainheadingorsubheading,trytocomposeanimportantquestionortwothatyoubelievethesectionwillanswer.Thispreviewquestionwillhelpfocusyourreadingofthesection.Itisalsoagoodideatokeepaskingyourselfquestionsasyouread.Thishabitfacilitatesactivereadingandlearning.

Read

Carefullyreadthesection.Readtounderstandconceptsandmajorpoints,andtrytofindtheanswertoyourpreviewquestion(s).Youmaywanttohighlightveryimportanttermsorexplanationsofconcepts,butdonotindiscriminantlyhighlighteverything.ReviseAfterreadingthesection,reviseyourquestion(s)tomoreaccuratelyreflectthesection'scontents.Thesequestionsshouldbeconcepttypequestionsthatforceyoutobringtogetheranumberofdetails.Theycanbewritteninthemarginsofyourtext.Record

Underlinetheinformationinthetextthatanswersyourquestions,ifyouhavenotalreadydoneso.Youmaywishtowritedowntheanswersinnoteformaswell.Thisprocesswillgiveyougoodmaterialtouseinpreparingforexams.Review

Reviewtheinformationbytryingtoansweryourquestionswithoutlookingatthetext.Ifthetexthasalistofkeywordsandasetofstudyquestions,besuretousetheseinyourreview.Youwillretainmuchmoreifyoureviewthematerialseveraltimes.1.1Whatisamicrobe?1.2TheimportanceofMicrobiology1.3Microbesinourlives1.4Thehistoryofmicrobiology1.5ImportanteventsinthedevelopmentofmicrobiologyCHAPTER1

MicroorganismsandMicrobiologyThewordmicrobe(microorganism)isusedtodescribeanorganismthatissosmallthat,normally,itcannotbeseenwithouttheuseofamicroscope.Viruses,bacteria,fungi,protozoaandsomealgaeareallincludedinthiscategory.1.1Whatisamicrobe?Ourworldispopulatedbyinvisiblecreaturestoosmalltobeseenwiththeunaidedeye.Theselifeforms,themicrobesormicroorganisms,maybeseenonlybymagnifyingtheirimagewithamicroscope.

MicrobialworldOrganisms

(living)Infectiousagents

(non-living)Prokaryotes(unicellular)eukaryotesvirusesviroidsprionsEubacteriaArchaeaAlgae(unicellularormulticellularFungi(unicellularormulticellularProtozoa(unicellular)OthermulticellularorganismsMostofthebacteria,proto-zoa,andfungiaresingle-celledmicroorganisms,andeventhemulticelledmicrobesdonothaveagreatrangeofcelltypes.Virusesarenotevencells,justgeneticmaterialsurroundedbyaproteincoatandincapableofindependentexistence.Thesizeandcelltypeofmicrobes

microbeApproximaterangeofsizesCelltypeViruses0.01-0.25µmAcellularBacteria0.1-10µmProkaryoteFungi2µm->1mEukaryoteProtozoa2-1000µmEukaryoteAlgae1µm-severalmetersEukaryoteMicrobesimpingeonallaspectsoflife,justafewofthesearelistedbelow:TheenvironmentMedicineFoodBiotechnologyResearch1.2TheimportanceofmicrobiologyTheenvironmentMedicineFood

BiotechnologyResearchPressheretocontinue

Microbesareresponsibleforthecyclingofcarbon,nitrogenandphosphors(geochemicalcycles),allessentialcomponentsoflivingorganisms(TopicFI).Theyarefoundinassociationwithplantsinsymbioticrelationships,maintainsoilfertilitvandmayalsobeusedtocleanuptheenvironmentoftoxiccompounds(bio-remediation;TopicsH6and14).Somemicrobesaredevastatingplantpathogens(TopicH7),whichdestroyimportantfoodcrops,butothersmayactasbiologicalcontrolagentsagainstthesediseases.Thedisease-causingabilityofsomemicrobessuchassmallpox.(Variolavirus;TopicKS),cholera(Vibriocholerabacteria;SectionF3)andmalaria(Plasmodiumprotozoa,TopicJ7)iswellknown.However,micro-organismshavealsoprovideduswiththemeansoftheircontrolintheformofantibiotics(TopicF7)andothermedicallyimportantdrugs.Microbeshavebeenusedforthousandsofyears,inmanyprocesses,toproducefood,frombrewingandwinemaking,throughcheeseproductionandbreadmaking,tothemanufactureofsoysauce(TopicF2).Attheotherendofthescale,microbesareresponsibleforfoodspoilage,anddisease-causingmicrobesarefrequentlycarriedonfood(TopicF5).Traditionallymicrobeshavebeenusedtosynthesizemanyimportantchemicalssuchasacetoneandaceticacid(TopicF2).Morerecentlyheadventofgeneticengineeringtechniqueshasledtothecloningofpharmaceuticallyimportantpolypeptidesintomicrobes,whichmayhenbeproducedonalargescale.Microbeshavebeenusedextensivelyasmodelorganismsfortheinvestigationofbiochemicalandgeneticalprocessesastheyaremucheasiertoworkwiththanmorecomplexanimalsandplants.Millionsofcopiesofthesamesinglecellcanbeproducedinlargenumbersveryquicklyandatlowcosttogiveplentyofhomogeneousexperimentalmaterial.Anadditionaladvantageisthatmostpeoplehavenoethicalobjectionstoexperimentswiththesemicroorganisms.MicrobiologyBacteriologyProtozoologyParasitologyMicrobialMorphologyMycologyVirologyPhycologyorAlgologyMicrobialphysiologyMicrobialtaxonomyMicrobialgeneticsMolecularbiologyMicrobialecologyThediscoveryofmicroorganismsThespontaneousgenerationconflictTherecognitionofmicrobialroleindiseaseThediscoveryofmicrobialeffectsonorganicandinorganicmatterThedevelopmentofmicrobiologyinthiscentury1.4ThehistoryofmicrobiologyThediscoveryofmicroorganismsThefirstpersontoaccuratelyobserveanddescribemicroorganismsAntonyvanLeeuwenhock(1632-1723)ThefirstpersontoobserveanddescribemicroorganismswastheamateurmicroscopistAntonyvanleeuwenhoekofDelft,Holland.Leeuwenkoekmadehissimple,single-lensmicroscopewhichcouldamplifytheobjectbeingviewed50–300times.Between1673–1723,hewroteaseriesofletterstotheRoyalSocietyofLondondescribingthemicrobesheobservedfromthesamplesofrainwater,andhumammouth.Leeuwenhoek’sdrawingsofbacteriafromthehumanmouth.Adrawingofoneofthemicroscopesshowingthelensa;mountingpinb;andfocusingscrewscandd.lensObjectbeingviewedadjustingscrewsFinalrefutationofspontaneousgeneration–birthofmicrobiologyasascienceDiscoveryoftheexistenceofanaerobiclife–fermentationVaccinesPasteurizationPasteur’scontributions:LouisPasteurworkinginhislaboratoryLouisPasteur(1822–1895)Pasteur(1857)demonstratedthatlacticacidfermentationisduetotheactivityofmicroorganisms.2.Pasteur(1861)conflictoverspontaneousgeneration–birthofmicrobiologyasascience3.Pasteur(1881)developedanthraxvaccine4.PasteurizationThespontaneousgenerationconflictSpontaneousgeneration–thatlivingorganismscoulddevelopfromnonlivingordecomposingmatter.Pasteur’sswanneckflasksusedinhisexperimentsonthespontaneousgenerationofmicroorganismsConclusion:Microorganismsarenotspontaneouslygeneratedfrominanimatematter,butareproducedbyothermicroorganismsRobertKockinhislaboratoryTherecognitionofmicrobialroleindiseaseRobertKock(1843–1910)Themicroorganismsmustbepresentineverycaseofthediseasebutabsentfromhealthyorganisms.Thesuspectedmicroorganismsmustbeisolatedandgrowninapureculture.Thediseasemustresultwhentheisolatedmicroorganismsisinoculatedintoahealthyhost.ThesamemicroorganismsmustbeisolatedagainfromthediseasedhostKock’spostulatesTheGoldenageofmicrobiologyKochandpureculturesFermentationandPasteurizationGermtheoryofdeseaseVaccinationBeijerinckmadefundamentalcontributionstomicrobialecology.HeisolatedAzotobacterandRhizobium.ThediscoveryofmicrobialeffectsonorganicandinorganicmatterTheRussianmicrobiologistWinograskydiscoveredthatsoilbacteriacouldoxidizeiron,sulfurandammoniatoobtainenergy,andalsoisolatednitrogen–fixingbacteria.SirAlexanderFlemingdiscoveredtheantibioticpenicillin.Hehadtheinsighttorecognizethesignificanceoftheinhibitionofbacterialgrowthinthevicinityofafungalcontaminantwhenmostotherscientistsprobablywouldhavesimplydiscardedthecontaminatedplates.AlexanderFleming(1881-1955)1676Leeuwenhoekdiscovers"animalcules"1.5Importanteventsinthedevelopmentofmicrobiology

2.1Overviewofthestructureofmicrobialcells2.2Procaryoticcellwall2.3Cytoplasmicmembrane2.4Cellulargeneticinformation2.5Cytoplasmicmatrix–RibosomeandInclusions2.6Componentsexternaltothecellwall2.7Bacterialendospores2.8ComparisonoftheprokaryoticandeukaryoticcellChapteroutlineAprocaryoticcellAeucaryoticcell

Overviewofcellstructure3.TheircellwallalmostalwayscontainthecomplexpolysaccharidepeptidoglycanTheprokaryoticcell1.Theirgeneticmaterial(DNA)isnotenclosedwithinamembraneandtheylackothermembrane–boundedorganelles2.TheirDNAisnotassociatedwithhistidine4.Theyareverysmall!!Size:

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

Acyanobacterium8x50umsizecomparisonofmicroorganismsVisibilityscaleMetersRelativesizeofMicrobesProkaryotesEukaryotesVirusesNakedeyeLightmicroscopeElectronmicroscopeacellincreasesinsize,itssurfacearea–to–volumeratiodecreasesSurfaceareaandvolumerelationshipsincellsspirallumShape:

Bacteriahaveafewbasicshapesspherical

coccusRod-shaped

bacillusThecellwallofthebacterialcellisacomplex,semi-rigidstructurethatisresponsibleforthecharacteristicshapeofthecell.Thecellwallsurroundstheunderlying,fragileplasma(cytoplasmic)membraneandprotectsitandinternalpartsofthecellfromadversechangesinthesurroundingenvironment.Almostallprokaryoteshavecellwalls.ProkaryoticcellwallGram+Gram-SchematicdiagramofbacterialcellwallsBacteriacanbedividedintotwomajorgroups,calledgram-positiveandgram-negative.Theoriginaldistinctionbetweengram-positiveandgram-negativewasbasedonaspecialstainingprocedure,theGramstainTheGram-positivecellwallhasapeptidoglycanlayerthatisrelativelythick(ca.40nm)andcomprisesapproximately90%ofthecellwall.ThecellwallsofmostGram-positiveeubacteriaalsohaveteichoicacids.Gram-positivecellwallStructureoftheRepeatingUnitinPeptidoglycanTheseconstituentsareconnectedtoformarepeatingstructure,theglycantetrapeptide.Peptidoglycaniscomposedoftwosugarderivatives,N-acetylglucosamine(NAG)andN-acetylmuramicacid(NAM),andasmallgroupofaminoacidsconsistingofL-alanine,D-alanine,D-glutamicacid,andeitherlysineordiaminopimelicacid(DAP).PeptideandglycanunitsareconnectedinformationofthepeptidoglycansheetGram-positiveBacteriafrequentlyhaveacidicpolysaccharidescalledteichoicacidsattachedtotheircellwall.Thetermteichoicacidsincludesallwall,membrane,orcapsularpolymerscontainingglycerophosphateorribitolphosphateresidues.ThesepolyalcoholsareconnectedbyphosphateestersandusuallyhaveothersugarsandD-alanineattached.

TeichoicacidsTeichoicacidsandlipoteichoicacidsarearrangedintheoverallwallstructureofgram-positiveBacteria.TeichoicacidLipoteichoicacidTheGram-negativecellwallisathinlayerattachedtoanoutermembranevialipoproteins.Theoutermembranecontainsphospholipidonitsinnersurfaceandlipopolysaccharide(LPS)onitsoutersurface.Thespacebetweentheoutermembraneandthecytoplasmicmembraneiscalledtheperiplasmicspace.TeichoicacidsdonotoccurinGram-negativebacterialcellwalls..

OsidechainCorepolysaccharideLipidAChemicalstructureofLipopolysaccharideMolecularmodelofE.colilipopolysaccharide

Thebondsbetweenthecarbohydratesinpseudopeptidoglycanareβ1-3insteadof'β1-4asinpeptidoglycan.

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

ProceduresofGramStainingGrampositiveorGramnegative?Morphologyofagram-positivebacterialcellStructureofcytoplasmicmembraneFunctionofcytoplasmicmembrane2.3CytoplasmicmembraneA.Thetypicalcytoplasmicmembraneofprokaryoticandeukaryoticcellsisalipidbilayer,asillustratedhereshowingtheorientationsofthehydrophilic(tanspheres)andhydrophobic(black)endsofphospholipidsthatmakeupthisstructure.B.Colorizedelectronmicrographof'thecytoplasmicmembrane(CM)ofthebacteriumBacillussubtilisrevealsthecharacteristicrailroadtrackappearanceofthislipidbilayer.StructureofcytoplasmicmembraneItisatypicalUNITMEMBRANE!Thecytoplasmicmembrane,ahighlyselectivebarrier,isconstructedprincipallyoflipid,withinwhichcertainproteinsareembedded.Membranescontainbothlipidsandproteins,althoughtheexactproportionsoflipidandproteinvarywidely.1.Permeabilitybarrier-preventsleakageandfunctionasgatewayfortransportofnutrientsintoandoutofthecell.2.Proteinanchor-siteofmanyproteinsinvolvedintransport,bioenergetics,andchemotaxis.3.Energyconservation-siteofgenerationanduseoftheprotonmotiveforce.

FunctionofmembraneIntracellularmembranesystemBacteriacellsdon’tcontainmembrane-enclosedorganelles.However,bacteriamayhavespecializedinvaginationsofthecytoplasmicmembrane.Theirfunctionmaybetoprovidealargermembranesurfaceforgreatermetabolicactivity.StructureofMesosomeMesosomemaybeinvolvedinwallformationduringdivisionorplayaroleinchromosomereplicationanddistributiontodaughtercells.Itmayalsobeinvolvedinsecretoryprocesses2.4CellulargeneticinformationBacterialChromosomeSupercoilingandchromosomestructureChromosomalcopynumberPlasmidsMicrographofabacteriumshowingthenucleoidregion(green)withinthecytoplasmwherethebacterialchromosomeoccursThebacterialchromosomeisacircularDNAmacromoleculeexceptinStreptomyces

whereitislinearandRhodobacter

sphaffoides,whichhastwoseparatechromosomes.

BacterialchromosomeThebacterialchromosomeisusuallyasinglecovalentlyclosedcircularmolecule.ThetermnucleoidisusedtodescribeaggregatedDNAintheprokaryoticcell.RangeofgenomesizesinvirousgroupsoforganismsandtheorganellesofeukaryaThebacterialchromosomeandsupercoiling:ExampleofE.colicellThereareover

50supercoileddomainintheE.colichromosome.ThetotalamountofDNAisabout4600kb.IfthetotalDNAisopenedandlinearized,itwouldbe1mminlength.Thethecellisonlyabout2-3umlong.SotopackagethismuchDNAintothecellrequiresthattheDNAbehighlysupercoiled.ElectronmicrographofanisolatednucleoidreleasedfromE.coli.

Chromosomecopynumber

Bacteriathatreproduceasexuallyaretypicallyhaploidingeneticcomplement.Rapidlygrowingcellscontainmorethan

1copyofthechromosome,andonlywhencellgrowthhasceaseddoesthechromosomenumberapproachonepercell.

Reproductionofabacterialcellrequiresthereplicationofthebacterialchromosome.ThemicrographshowsthesequenceofsynthesisofnewcircularloopsofdoublehelicalDNA.Bacterianormallyreproducebybinaryfission.Theinwardgrowthoftheseptumdividestheparentcelltoproducetwoequal-sizedprogenycells.Plasmidsdon’tcontainthegeneticinformationfortheessentialmetabolicactivitiesofthecell,buttheygenerallydocontaingeneticinformationforspecialfeatures.

PlasmidProkaryoticcellshavesmallextra-chromosomalgeneticelementscalledplasmids.ResistantplasmidsColplasmidsConjugativeplasmidsMetabolicplasmidsMajortypesofplasmids

2.5Cytoplasmicmatrix–RibosomeandInclusionsAlleucaryoticandprocaryoticcellscontainribosomes,whichfunctionasthesitesofproteinsynthesis.Ribosomesarecomposedoftwosubunits

Procaryoticribosomesarecalled70Sribosomes,andthoseofeucaryoticcellsareknownas80SribosomesRibosomesTheletterSreferstoSvedbergunits,whichindicatetherelativerateofsedimentationduringultra-high-speedcentrifugationWithinthecytoplasmofprocaryotic(andeucaryotic)cellsareseveralkindsofreservedeposits,knownasinclusions.Someinclusionsarecommontoawidevarietyofbacteria,whereasothersarelimitedtoasmallnumberofspeciesandthereforeserveasabasisforidentification.Amongthemoreprominentbacterialinclusionsarethefollowing:Carbonstoragepolymers–PHBandglycogenPhosphatepolymersSulfurGranulesGasVacuolesINCLUSIONSPolyhydroxybutyricacid(PHB)PHBisalipidlikecompound-oneofthemostcommoninclusionbodiesinprokaryoticorganisms.PHBiscommonlyfoundasastoragematerialanduniquetobacteria

Glycogenisastarchlikepolymerofglucosesubunits.GlycogengranulesareusuallysmallerthanPHBgranules.AVibriospeciesManymicroorganismsaccumulategranulesofpolyphosphate,whicharelargereservesofinorganicphosphatesthatcanbeusedinthesynthesisofATPPolyphosphategranule

inabacterialcellAPseudomonasspeciesThesulfurglobulesinsidethecellsofpurplesulfurbacteriumChromatiumbuderiSomebacteria,includingmanyphotosyntheticbacteria,accumulateelementalsulfurgranulesasaresultoftheirmetabolism.Gasvacuoles(blue)andstoragegranules(red)inthecyanobacteriumMicrocystisTheformationofgasvacuolesbyaquaticbacteriaprovidesamechanismforadjustingthebuoyancyofthecell.Manyaquaticcyanobacteriausetheirgasvacuolestomoveupanddowninthewatercolumn.2.6ComponentsexternaltothecellwallFlagellaFimbriaeandpiliCapsulesandslimelayersMotilityallowsthecelltoreachdifferentregionsofitsenvironment.Inthestruggleforsurvival,movementtoanewlocationmaymeanthedifferencebetweensurvivalanddeathofthecell.But,asinanyphysicalprocess,cellmovementiscloselytiedtoanenergyexpenditure,andthemovementofflagellaisnoexception.

Manyprokaryotesaremotile,andthisabilitytomoveindependentlyisusuallyduetoaspecialstructure,theflagellum(plural,flagella).Fourbasictypesofflagellararrangementsa,monotrichousb,amphitrichousc,lophotrichousd,peritrichousFlagellaarearrangeddifferentlyondifferentbacteria.Inpolarflagellationtheflagellaareattachedatoneorbothendsofthecell.Occasionallyatuft(group)offlagellamayariseatoneendofthecell,anarrangementcalledlophotrichous.Inperitrichousflagellationtheflagellaareinsertedatmanyplacesaroundthecellsurface(perimeans"around").Thetypeofflagellation,polarorperitrichous,isoftenusedasacharacteristicintheclassificationofbacteria.TheflagellumofaGram-negativebacteriumThefilamentofbacterialflagellaiscomposedofsubunitsofaproteincalledflagellin.

Thebaseoftheflagellumisdifferentinstructurefromthatofthefilament.Thereisawiderregionatthebaseoftheflagellumcalledthehook.Thehookconsistsofasingletypeofproteinandfunctionstoconnectthefilamenttothemotorportionoftheflagellum.

Thebasalbodyisanchoredinthecytoplasmicmembraneandcellwall.Thebasalbodyconsistsofasmallcentralrodthatpassesthroughasystemofrings.Ingram-negativeBacteria,anouterringisanchoredinthelipopolysaccharidelayerandanotherinthepeptidoglycanlayerofthecellwall,andaninnerringislocatedwithinthecytoplasmicmembrane.Ingram-positiveBacteria,whichlacktheouterlipopolysaccharidelayer,onlytheinnerpairofringsispresent.SurroundingtheinnerringandanchoredinthecytoplasmicmembraneareapairofproteinscalledMot.Theseproteinsactuallydrivetheflagellarmotorcausingatorquethatrotatesthefilament.Afinalsetofproteins,calledtheFliproteinsfunctionasthemotorswitch,reversingrotationoftheflagellainresponsetointracellularsignals.Themovementofaprocaryoticflagellumresultsfromrotationofitsbasalbodyandissimilartothemovementoftheshaftofanelectricmotor.Bacterialcellscanalterthespeedanddirectionofrotationofflagellaandthusarecapableofvariouspatternsofmotility.Fimbriaecanbeevenlydistributedovertheentiresurfaceofthecell.Theycannumberanywherefromafewtoseveralhundredpercell.Fimbriaeallowacelltoadheretosurfacesincludingthesurfacesofothercells.Piliareusuallylongerthanfimbriaeandnumberonlyoneortwopercell.PilifunctiontojoinbacterialcellspriortothetransferofDNAfromonecelltoanother.

FpilusManyprokaryoticorganismssecreteontheirsurfacesslimyorgummymaterials.Avarietyofthesestructuresconsistofpolysaccharide,andafewconsistofprotein.Thetermscapsuleandslimelayerarefrequentlyusedtodescribepolysaccharidelayers.Demonstrationofthepresenceofacapsuleisusuallybymeansofnegativestaining

CapsulesandSlimeLayersManyprokaryotescontainacellsurfacelayercomposedofatwo-dimensionalarrayofprotein.TheselayersarecalledS-layers.S-layershavebeendetectedinrepresentativesofvirtuallyeveryphylogeneticgroupingofBacteriaandarenearlyuniversalamongArchaea.InsomespeciesofArchaeatheS-layerisalsothecellwall.ThemajorfunctionofS-layersisunknown.However,astheinterfacebetweenthecellanditsenvironmentitislikelythatincellsthatproducethemtheS-layeratleastfunctionsasanexternalpermeabilitybarrier,allowingthepassageoflow-molecular-weightsubstanceswhileexcludinglargemolecules.ParacrystallineSurfaceLayers(S-Layers)2.7BacterialendosporesCertainspeciesofbacteriaproducespecialstructurecalledendospores.Theyareveryresistanttoheatandcannotbedestroyedeasily,evenbyharshchemicals.Endosporesarealsoresistanttootherharmfulagentssuchasdry