微生物学英文课件3

Chapter 3The ProkaryotesChapterOutline3.1Bacteria3.2Actinomycetes3.3Cyanobacteria3.4Archaeobacteria3.5Otherprokaryotes3.6ClassificationofbacteriaConceptsMicroorganismsaretoosmalltobeseenwithouttheuseofamicroscope.Thetechniques-suchassterilizationandtheuseofculturemediumarerequiredtoisolateandgrowthesemicrobes.Bacteriamaybespherical(cocci),rod-shaped(bacilli),spiral,orfilamentous.Mostbacteriacanbedividedintogram-positiveandgram-negativegroupsbasedontheircellwallstructureandresponsetotheGramstain.Bacteriasuchasmycoplasmaslackacellwall.Size,Shape,and Arrangement of Bacterial CellsThey have a few basic shapes-spherical coccus(plural,cocci,meaning berries),rod-shaped bacillus(plural,bacilli,meaning little staffs),and spiral.Cm=10-2metermm=10-3meterm=10-6meternm=10-9meter3.1BacteriaMost bacteria fall within a rangefrom 0.2 to 2.0 m in diameter and from 2 to 8m in length.Morphology(shape)Chemical composition(often detectedbystainingreactions)NutritionalrequirementsBiochemicalactivitiesSourceofenergy(sunlightorchemicals)How to identify an unknown bacterial species?Factors:Arrangement of Spherical Bacterial CellsThe Micrococcaceae1.Micrococcus 2.Staphylococcus 3.StreptococcusThefamilyMicrococcaceae containsgram-positivecocci,0.5-2.5mindiameter,thatdivideinmorethanoneplanetoformregularorirregularclustersofcells.Allareaerobicorfacultativelyanaerobic.Thepeptidoglycandi-aminoacidisL-lysine.The three most important genera are:Micrococcusaerobic,gram-positive,catalasepositive,cellarrangesmainlyinpairs,tetrads,orirregularclusters,nonmotile.Theyareoftenyellow,orangeorredincolorStaphylococcus-facultativelyanaerobic,gram-positive,usuallyformirregularclusters,nonmotile,catalasepositivebutoxidasenegative,fermentglucoseanaerobically.staphylococcistaphylococciStreptococcus -facultativelyanaerobicormicroaerophilic,catalasenegative,gram-positive,Cellarrangesinpairsorchains,usuallynonmotile,Afewspeciesareanaerobicratherthanfacultative.Bacillidivideonlyacrosstheirshortaxis,sotherearefewergroupingsofbacillithanofcocci.Rod-shaped bacteriaSingle bacillusDiplobacillistreptobacilliCoccobacillusClostridium botulinusC.butyricumC.aceticumC.tetaniC.putrificumBacillus subtilis,B.MycoidesB.PastturiiB.megateriumB.ThuringiensisB.AnthracisB.BotulinusB.cereus Spore-forming rod shaped bacteria Almost all Spore-forming bacteria are Gram+Clostridium AnaerobicBacillus AerobicNonspore-forming rod shaped bacteriaMost nonspore forming rod shaped bacteria are Gram-Representatives:Escherchia coliAlcaligenesProteusFlavobacteriaPseudomonasRhizobiumAzotobacterVibrio,Spirillum and SpirocheteSomebacteriaareshapedlikelongrodstwistedintospiralsorhelices;theyarecalledvibrios(likecommasorincompletespirals),spirillaifrigidandspirocheteswhenflexable.vibriospirillumspirochete3.2ActinomycetesActinomycetes are filamentous bacteria.Theirmorphology resembles that of the filamentousfungi;however,the filaments of actinomycetesconsistof procaryoticcells.Someactinomycetesresemble molds by forming externally carriedasexualsporesforreproduction.Filamentous,HighG+Ccontent,Gram-positive(6378%GC)Chain of conidiosporesAgar surfaceSubstrate myceliumAerial hyphaeThe cross section of an actinomycete colony showing the substrate mycelium and aerial mycelium with chains of conidiosporesVarioustypesofspore-bearingstructuresonthestreptomycesRepresentivegenera:StreptomycesNocardiaActinomycesMicromonosporaStreptosporangiumActinoplanesFrankiaOver500distinctantibioticsubstanceshavebeenshowntobeproducedbystreptomycete.Mostantibioticsareefficientagainstdifferentbacteria.Morethan50antibioticshavebeenusedinhumanandveterinarymedicine,agricultureandindustryAntibioticsActinomycetesChain of conidiosporesAgar surfaceSubstrate myceliumAerial hyphaeThecrosssectionofanactinomycetecolonyshowingthesubstratemyceliumandaerialmyceliumwithchainsofconidiosporesVarious types of spore-bearing structures on the streptomycesStreptomycesspores,calledconidia,arenotrelatedinanywaytotheendosporesofBacillus and Clostridium becausethestreptomycetesporesareproducedsimplybytheformationofcross-wallsinthemultinucleatesporophoresfollowedbyseparationoftheindividualcellsdirectlyintospores.Ecology and isolation of Streptomyces:AlkalineandneutralsoilsaremorefavorableforthedevelopmentofStreptomyces thanareacidsoils.Streptomyces requirealowerwaterpotentialforgrowththanmanyothersoilbacteria.MediaoftenselectiveforStreptomyces containtheusualassortmentofinorganicsaltsThestreptonycetesarealargegroupoffilamentous,grampositivebacteriathatformsporesattheendofaerialfilaments.TheyhavethehighestGCpercentageintheDNAbasecompositionofanybacteriaknown.ManyclinicallyimportantantibioticshavecomefromStreptomycetesspeciesConcept3.3CyanobacteriaThecyanobacteriahavetypicalprokaryoticcellstructuresandanormalgram-negativecellwall.Theyrangeindiameterfromabout110mandmaybeunicellularorformfilaments.Theyhavechlorophyllandcarryoutoxygen-producingphotosynthesis,muchasplantsandtheeukaryoticalgaedo.Filamentous Cyanobacterium,Anabaenasp.(SEMx5,000)Nonfilamentous cyanobacteriaThemorphologicaldiversityofthecyanobacteriaisconsiderable.Bothunicellularandfilamentousformsareknown,andconsiderablevariationwithinthesemorphologicaltypesoccurs.Heterocystshaveintercellularconnectionswithadjacentvegetativecells,andthereismutualexchangeofmaterialsbetweenthesecells,withproductsofphotosynthesismovingfromvegetativecellstoheterocystsandproductsofnitrogenfixationmovingfromheterocyststovegetativecells.Photosynthesis Nitrogen fixationMain function of CyanobacteriaThecyanobacteriaarethelargestandmostdiversegroupofphotosyntheticbacteria.Thestructureandphysiologyoftheheterocystensuresthatitwillremainanaerobic;itisdedicatedtonitrogenfixation.Itshouldbenotedthatnitrogenfixationalsoiscarriedoutbycyanobacteriathatlackheterocysts.Cycnobacteriaarecapableofconsiderablemetabolicflexibility.Thenutritionofcyanobacteriaissimple.Vitaminsarenotrequired,andnitrateorammoniaisusedasnitrogensource.Nitrogen-fixingspeciesarecommon.Mostspeciestestedareobligatephototrophs,However,somecyanobacteriaareabletogrowinthedarkonorganiccompounds,usingtheorganicmaterialasbothcarbonandenergysource.Physiology of cyanobacteria:Manycyanobacteriaproducepotentneurotoxins,andduringwaterbloomswhenmassiveaccumulationsofcyanobacteriamaydevelop,animalsingestingsuchwatermaysuccumbrapidly.Problems!3.4 The Archaebacteria Althougharchaebacteriaareclassifiedasprocaryotes,thesecellsappeartobefundamentallydifferentfromtypicaIbacteriaorcyanobacteria.Infact,theyrepresentacelltypethatseemstobeneithereucaryoticnoreubacterial.Theyareabout1micrometer(um)indiameter,thesizeoftypicalprocaryotes.Theylackmembrane-boundorganelles.Theyhavenuclearbodies(nucleoids)ratherthantrue,menbraneeboundnuclei.Theirribosomesare70S,thesizeofthosefoundintypicalprokaryotes.The archaebacteria have the following unique combination of traits:Prokaryotic traits:Theircellwallscompletelylackpeptidoglycan.Theirproteinsynthesismachineryissensitivetoinhibitorsthattypicallyaffectonlyeukaryotesandisresistanttomanyinhibitorsthataffectprokaryotes.Someoftheirproteins,pigments,andbiochemicalprocessescloselyresemblethosefoundineukaryoticcells.Eukaryotic traits:Archaebacteriaincludethreegroups:1.Themethanogens,strictanaerobesthatproducemethane(CH4)fromcarbondioxideandhydrogen.2.Extremehalophiles,whichrequirehighconcentrationsofsaltforsurvival.3.Thermoacidophiles,whichnormallygrowinhot,acidicenvironments.MethanogenicbacteriaarestrictanaerobesthatobtainenergybyconvertingC02,H2,formate,acetate,andothercompoundstoeithermethaneormethaneandC02.C02+4 H2CH4+2 H2OCH3 C00 HC02+CH4Methanogenesis may eventually serve as a major source of pollution-free energy?!Sewagetreatmentplantsusethemethaneproducedtogenerateheatandelectricity.They are gram-negative,aerobic,irregularlylobed spherical bacteria with a temperatureoptimumaround70-800CandapHoptimumof2to3.Theircellwallcontainslipoproteinandcarbohydratesbutlackspeptidoglycan.ExtremelythermophilicbacteriaTheirmostdistinctivecharacteristicistheirrequirementofahighconcentrationofsodiumchlorideforgrowth.Theyareaerobicchemoheterotrophswithrespiratorymetabolismandrequirecomplexnutrients,usuallyproteinsandaminoacids,forgrowth.Extremehalophilicbacteria3.5OtherprokaryotesRickettsia Chlamydia Mycoplasma Bdellovirio3.Manyspeciesofthemcausediseaseinhumansandotheranimals.Rickettsia1.0.2-0.5mindiameter.obligateintracellularparasites.Themajorityofthemaregram-negativeandmultiplyonlywithinhostcells.2.Binaryfissionwithinhostcells.TheylacktheenzymaticcapabilitytoproducesufficientamountsofATPtosupporttheirreproduction.TheyobtaintheATPfromhostcells.ChlamydiaObligateintracellularparasites,unabletogeneratesufficientATPtosupporttheirreproduction.Gram-negativeandcelldividesbybinaryfissionCausehuman respiratoryandgenitourinarytractdisease,andinbirdstheycauserespiratorydisease.MycoplasmaDiameter=0.1-0.25m.Theylackcellwall,areboundedbyasingletriple-layeredmembrane.Theyarethesmallestorganismscapableofself-reproduction.Severalofthemcausediseasesinhumans.(pneumonia,respiratorytractdisease)Thecolonyis“friedegg”appearance.Bdellovirio3.6Classificationofbacteria4.NUMERICALTAXONOMY1.MORPHOLOGICALCHARACTERISTICS2.DIFFERENTIALSTAINING3.NUCLEICACIDHYBRIDIZATIONProtistaProkaryotaeFive-kingdom system is a commonly accepted system of classificationFungiPlantAnimalArchaebacteriaEubacteriaEukaryotesUniversalPhylogeneticTreederivedfromcomparativesequencingof16Sor18SRNA.Notethethree majordomainsoflivingorganisms.Divisions and Classes in the Kingdom Procaryotae(Monera)Identified by Common NamesDIVISIONCLASSNonphotosyntheticbacteriaTypicalgram-negativecellwallAnaerobicphotosyntheticbacteriaCyanobacteriaTypicalgram-positivecellwallWall-lessprocaryotesUnusualwallsRodsandcocciActionmycetesandrelatedorganismsMycopeanasArchaeobacteriaThetaxonomicclassificationschemeforbacteriamaybefoundinBergeys Manual of Systematic Bacteriology.In Bergeys Manual,bacteria are divided intofour divisions.Three divisions consist ofeubacterialcells,andthefourthdivisionconsistsofthearchaeobacteria.EachdivisionisdividedintoclassesStrainisagroupofcellsallderivedfromasinglecell.ClassesaredividedintoordersfamiliesgeneraspeciesBacterial species isdefinedsimplyasapopulationofcellswithsimilarcharacteristics.Morphologicalcharacteristicsareusefulinidentifyingbacteria.Forexample,differencesinsuchstructuresasendosporesorflagellacanbehelpful.However,manymicroorganismsappeartoosimilartobeclassifiedbytheirstructures.MORPHOLOGICALCHARACTERISTICS(ForexampleGramstaining)Mostbacteriaare either gram-positive or gram-negative.Butnotusefulinidentifyingeitherthewall-less bacteria or the archaeobacteria withunusualwalls.DIFFERENTIALSTAININGNUCLEICACIDHYBRIDIZATIONoThesimilaritybetweengenomescanbecomparedmoredirectlybyuseofnucleicacidhybridizationstudies.oIfamixtureofsingle-strandedDNAformedbyheatingdsDNAiscooledandheldatatemperaturebelowtheTm,strandswithcomplementarybasesequenceswillreassociatetoformstabledsDNA,whereasnoncomplementarystrandswillremainsingle.NUMERICALTAXONOMYThedevelopmentofcomputershasmadepossiblethequantitativeapproachknownasnumerical taxonomy.Informationaboutthepropertiesoforganismsisconvertedintoaformsuitablefornumericalanalysisandthencomparedbymeansofacomputer.Theresultingclassificationisbasedongeneralsimilarityasjudgedbycomparisonofmanycharacteristics,eachgivenequalweight.REVIEW QUESTIONS1.Describethecharacteristicsmostimportantindistinguishingbetweenmembersofthefollowinggroupsofgenera:StaphylococcusandStreptococcus,BacillusandClostridium.2.HowdosporesandtheprocessofsporulationinaStreptomycesspeciesdifferfromthatinaBacillusspecies?3.Whyisnitrogenfixationanoxygen-sensitiveprocess?Howarecyanobacteria abletofixnitrogenwhentheyalsocarryoutoxygenicphotosynthesis?4.Whatisa heterocyst andwhatisitsfunction?5.Howwouldyouselectthebestfeaturestouseinidentificationofunknownprocaryotesanddeterminationofrelatedness?