华中农业大学微生物英文版

Chapter9

MicrobialEcologyMicrobialecology=?EnvironmentalmicrobiologyThetermmicrobialecologyisnowusedinageneralwaytodescribethepresenceanddistributionsofmicroorganisms.Microbialecologyisthethestudyofthebehaviorandactivitiesofmicroorganismsintheirnaturalenvironments.Environmentalmicrobiology,incomparison,relatesprimarilytoall-overmicrobialprocessesthatoccurinasoil,waterorfood,asexamples.Itisnotconcernedwiththeparticularmicroenvironmentwherethemicroorganismsactuallyarefunctioning,butwiththebroader-scaleeffectsofmicrobialpresenceandactivities.9.1Microorganismsinnatureecosystem9.2Microbialpopulationinteractions9.3Biogeochemicalcycles9.4Plant-microbeinteractions9.5BioremediationChapter9

MicrobialEcology9.1Microorganismsinnatureecosystem1.Microorganismsandmicroenvironment2.TerrestrialEnvironments3.FreshwaterEnvironments4.MarineEnvironments

9.1.1MicroorganismsandmicroenvironmentpopulationsguildscommunitiesecosystemMetabolicallyrelatedpopulationsconstitutegroupingscalledguilds.Setsofguildsconductingcomplementaryphysiologicalprocessesinteracttoformmicrobialcommunities.Inamicrobialecosystemindividualcellsgrowtoformpopulations.Community3Microbialcommunitiestheninteractwithcommunitiesofmacroorganismstodefinetheentireecosystem.Thedistributionofmicroorganismsinnatureecosystemdependsontheresources(nutrients)availableandonthegrowthconditions.Temperature,pH,wateravailability,light,oxygenofahabitatdefinethenicheforeachparticularmicroorganism.

Soilparticlesarenothomogeneousintermsoftheiroxygencontent.Theouterzonesofasmallsoilparticlemaybefullyoxic,whereasthecenter,onlyaveryshortdistanceaway,canremaincompletelyanoxic.Asoilaggregatecomposedofmineralandorganiccomponents,showingthatlocalizationofsoilmicrobes.Veryfewmicroorganismsarefoundfreeinthesoilsolution;mostofthemoccurasmicrocoloniesattachedtothesoilparticles.9.1.2.TerrestrialEnvironmentsProportionofdifferentsoilmicroorganismsinsoilMicrobialnumberandbiomassincultivatedfieldsoil（15cm）MicrobesNumbers/gBiomass(g/m3）Bacteria108160Fungi105200Actinomycetes105-106160Algae104-10532Protozoa10438AgrobacteriumAlcaligenesArthrobacterBacillusCaulobacterCellulomonasClostridiumCorynebacteriumFlavobacteriumMicrococcusMycobacteriumPseudomonasStaphylcoccusMaintypesofsoilmicroorganismsTherhizosphereisthesoilregioninclosecontactwithplantroots.

Withintherhizosphere,theplantrootsexertadirectinfluenceonthesoilbacteria.Thisinfluenceisknownastherhizosphereeffect.Intherhizosphere,microbialpopulationsreachmuchhigherdensitiesintherhizospherethaninthefreesoil.

RhizosphereEffect(R/Sratio)(1)removinghydrogensulfide,whichistoxictotheplantroots(2)increasingsolubilizationofmineralnutrientsneededbytheplantforgrowth(3)synthesizingvitamins,aminoacids,auxins,gibberellinsthatstimulateplantgrowth(4)antagonizingpotentialplantpathogensthroughcompetitionandtheproductionofantibioticsMicrobialpopulationsintherhizospheremaybenefittheplantby:1，neutralism(中性关系)2，commensalism(偏利关系)3，synergism(协同关系)4，mutualism(互惠关系)5，competition(竞争关系)6，antagonism(拮抗关系)7，parasitism(寄生关系)8，predation(捕食关系)9.2MicrobialpopulationinteractionsNeutralism,thereisnoanyphysiologicaleffectbetweenthepopulations.Commensalism

isaunidirectionalrelationshipbetweenpopulationsinwhichonepopulationbenefitsandtheotheroneisunaffected.Synergism

indicatesthatbothpopulationsbenefitfromtherelationshipbuttheassociationisnotobligatory.Bothpopulationsarecapableofsurvivingindependently.MutualismSymbiosisisanobligatoryinterrelationshipbetweentwopopulationsthatbenefitsbothofthem.Lichensiscomposedofafungusandanalga.Competitionoccurswhentwopopulationsarestrivingforthesameresourceofnutrientsorthehabitat.Antagonism

occurswhenonepopulationproducesasubstrateinhibitorytoanotherpopulation.Parasitism,theparasitepopulationisbenefitedandthehostpopulationisharmed.Predationisawidespreadphenomenonwherethepredatorengulfsorattackstheprey.Thepreycanbelargerorsmallerthantheprey,andthisnormalresultsinthedeathoftheprey.Classificationofpopulationinteraction0,Noeffect;+,positiveeffect;-,negativeeffect.

EFFECTOFINTERACTIONNAMEOFINTERACTIONPOPULATIONAPOPULATIONBNeutralismCommensalismSynergismMutualismCompetitionAmensalismParasitismPredation00++-0or+++0+++----9.3Biogeochemicalcycles1.Carboncycle2.Nitrogencycle3.Sulfurcycle4.IroncycleCarboncycleCarboncycleCarbondioxideisincorporated,orfixed,intoorganiccompoundsbysuchphotoautotrophsascyanobacteria,greenplants,algae,andgreenandpurplesulfurbacteria.Chemoheterotrophsconsumetheorganiccompounds,animalseatphotoautotrophs,especiallygreenplants,andmayinturnbeeatenbyotheranimals.Whentheorganismsdie,theorganiccompoundsoftheirbodiesaredepositedinthesoilandaredecomposedbymicroorganisms,principallybybacteriaandfungi.Duringthisdecomposition,carbondioxideisreturnedtotheatmosphere.NitrogencycleProteinsfromdeadcellsandwasteproducts

MicrobialdecompositionAminoacidsAminoacidsAmmonia(NH3)ammonificationAlmostallthenitrogeninthesoilexistsinorganicmolecules,primarilyinproteins.Whenanorganismdies,theprocessofmicrobialdecompositionresultsinthehydrolyticbreakdownofproteinsintoaminoacids.

Theaminogroupsofaminoacidsareremovedandconvertedintoammonia(NH3).Ammonificationisbroughtaboutbynumerousbacteriaandfungi.

NH4+N02-NitrosomonasAmmoniumionNitriteionN02-N03-NitriteionNitrateionNitrobacterNitrificationinvolvestheoxidationoftheammoniumiontonitrateThegeneraNitrosomonasandNitrobacterareautotrophicnitrifyingbacteria.Theseorganismsobtainenergybyoxidizingammoniaornitrite.Inthefirststage,Nitrosomonasoxidizesammoniumtonitrites.Inthesecondstage,suchorganismsasNitrobacteroxidizenitritestonitrates

KeyprocessesandprokaryotesinthenitrogencycleProcessesExampleorganismsNitrification(NH4+→NO3-)NH4+→NO2-NitrosomonasNO2-→NO3-NitrobacterDenitrification(NO3-→N2)

Bacillus,Pseudomonas

N2Fixation(N2+8H→NH3+H2)

Free-living

AerobicAzotobacter

CyanobacteriaAnaerobicClostridium,purplegreenbacteriaSymbioticRhizobium

Bradyrhizobium.FrankiaAmmonification(organic-N→NH4+)

ManyorganismscandothisSulfurcycleKeyprocessesandprokaryotesinthesulfurcycleProcessesOrganismsSulfide/sulfuroxidation(H2S→S0→

SO42-)AerobicSulfurchemolithotrophs(Thiobacillus,Beggiatoa,manyothers)AnaerobicPurpleandgreenphototrophicbacteria,somechemolithotrophsSulfatereduction(anaerobic)(SO42-→H2S)

Desulfovibrio,DesulfobacterSulfurreduction(anaerobic)(S0→H2S)

Desulfuromonas,manyhyperthermophilicArchaeaSulfurdisproportionation(S2O32-→H2S+SO42-)

DesulfovibrioandothersOrganicsulfurcompoundoxidationorreduction(CH3SH→CO2+H2S)(DMSO→DMS)Desulfurylation(organic-S→H2S)Manyorganismscandothis9.4Plant-microbeinteractions1.LichensandMycorrhizas2.Theplantenvironment3.RootnodulebacteriaandsymbiosiswithlegumesLichensLichensareleafyorencrustinggrowthsthatarewidespreadinnatureandareoftenfoundgrowingonbarerocks,treetrunks,houseroofs,andsurfacesofbaresoils.Thelichenplantconsistsofasymbiosisoftwoorganisms,afungusandanalga.Lichensconsistofatightassociationofmanyfungalcellswithinwhichthealgalcellsareembedded.MycorrhizasMycorrhizaliterallymeans"rootfungus"andreferstothesymbioticassociationthatexistsbetweenplantrootsandfungi.

Probablytherootsofthemajorityofterrestrialplantsaremycorrhizal.Therearetwoclassesofmycorrhizae:ectomycorrhizae,inwhichfungalcellsformanextensivesheatharoundtheoutsideoftherootwithonlylittlepenetrationintotheroottissueitself,andendomycorrhizae,inwhichthefungalmyceliumisembeddedwithintheroottissue.Mycorrhizas

TypeofMycorrhizas:EctomycorrhizaandEndomycorrhizaMorphologyandFunctionofMycorrhizalInfectionMycorrhizaandPlantNutritionApplicationPotentialofVAMinAgriculturalpracticeandEcosystemDevelopmentandApplicationofMolecularProbesConstructionandAnalysisofGenomicLibrary

MycorrhizasEctomycorrhizasEndomycorrhizasEctendomycorrhizasFunctionsofmycorrhizaRootNoduleBacteriaandSymbiosiswithLegumes

StagesinNoduleFormationBiochemistryofNitrogenFixationinNodulesGeneticsofNoduleFormation:nodGenesGeneticCooperativityintheRhizobium-legumeSymbiosisConstructionandApplicationofGenetic-engineeredRhizobiumSymbiosisofFrankiaandNon-leguminousPlant

MorphologyandPhysiologicalCharacteristicofFrankiaHostsApplicationPotential8.5Bioremediation1.Pollutants2.MeansofbioremediationPollutants1,Microorganismsareanimportantpartofecosystems2,Microbialcommunitiesarecomplex3,Microbialgrowthrequiresnutrientsandallofwhichmustbepresentinusableforms4,Mostmicroorganismsnormallyassociatedwithhigherorganismsandthosegrowninthelab.tendtobelessabletocompeteandsurviveinsoilsandwaters5,ExtremeenvironmentsrestricttherangeofmicrobialtypeswhichareabletosurviveandfunctionConceptsMicroorganismsinNatureDis