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1、Chapter 9 Microbial EcologyMicrobial ecology=?Environmental microbiologyThe term microbial ecology is now used in a general way to describe the presence and distributions of microorganisms.Microbial ecology is the the study of the behavior and activities of microorganisms in their natural environmen
2、ts.Environmental microbiology,in comparison,relates primarily to all-over microbial processes that occur in a soil,water or food,as examples.It is not concerned with the particular microenvironment where the microorganisms actually are functioning,but with the broader-scale effects of microbial pres
3、ence and activities.9.1 Microorganisms in nature ecosystem9.2 Microbial population interactions9.3 Biogeochemical cycles9.4 Plant-microbe interactions9.5 BioremediationChapter 9 Microbial Ecology9.1 Microorganisms in nature ecosystem1.Microorganisms and microenvironment2.Terrestrial Environments3.Fr
4、eshwater Environments4.Marine Environments 9.1.1 Microorganisms and microenvironmentpopulationsguildscommunitiesecosystemMetabolically related populations constitute groupings called guilds.Sets of guilds conducting complementary physiological processes interact to form microbial communities.In a mi
5、crobial ecosystem individual cells grow to form populations.Community 3Microbial communities then interact with communities of macroorganisms to define the entire ecosystem.The distribution of microorganisms in nature ecosystem depends on the resources(nutrients)available and on the growth condition
6、s.Temperature,pH,water availability,light,oxygen of a habitat define the niche for each particular microorganism.Soil particles are not homogeneous in terms of their oxygen content.The outer zones of a small soil particle may be fully oxic,whereas the center,only a very short distance away,can remai
7、n completely anoxic.A soil aggregate composed of mineral and organic components,showing that localization of soil microbes.Very few microorganisms are found free in the soil solution;most of them occur as microcolonies attached to the soil particles.9.1.2.Terrestrial EnvironmentsProportion of differ
8、ent soil microorganisms in soilMicrobial number and biomass in cultivated field soil（15 cm）MicrobesNumbers/gBiomass(g/m3）Bacteria108160Fungi105200Actinomycetes105-106160Algae104-10532Protozoa10438AgrobacteriumAlcaligenesArthrobacterBacillusCaulobacterCellulomonasClostridiumCorynebacteriumFlavobacter
9、iumMicrococcusMycobacteriumPseudomonasStaphylcoccusMain types of soil microorganismsThe rhizosphere is the soil region in close contact with plant roots.Within the rhizosphere,the plant roots exert a direct influence on the soil bacteria.This influence is known as the rhizosphere effect.In the rhizo
10、sphere,microbial populations reach much higher densities in the rhizosphere than in the free soil.Rhizosphere Effect (R/S ratio)(1)removing hydrogen sulfide,which is toxic to the plant roots1.(2)increasing solubilization of mineral nutrients needed by the plant for growth 2.(3)synthesizing vitamins,
11、amino acids,auxins,gibberellins that stimulate plant growth3.(4)antagonizing potential plant pathogens through competition and the production of antibiotics Microbial populations in the rhizosphere may benefit the plant by: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
12、，competition (竞争关系)6，antagonism (拮 抗关系)7，parasitism (寄生关系)8，predation (捕食关系)9.2 Microbial population interactionsNeutralism,there is no any physiological effect between the populations.Commensalism is a unidirectional relationship between populations in which one population benefits and the other on
13、e is unaffected.Synergism indicates that both populations benefit from the relationship but the association is not obligatory.Both populations are capable of surviving independently.MutualismSymbiosis is an obligatory interrelationshipbetween two populations that benefits both ofthem.Lichens is comp
14、osed of a fungus and an alga.Competition occurs when two populations are striving for the same resource of nutrients or the habitat.Antagonism occurs when one population produces a substrate inhibitory to another population.Parasitism,the parasite population is benefited and the host population is h
15、armed.Predation is a widespread phenomenon where the predator engulfs or attacks the prey.The prey can be larger or smaller than the prey,and this normal results in the death of the prey.Classification of population interaction0,No effect;+,positive effect;-,negative effect.EFFECT OF INTERACTION NAM
16、E OF INTERACTION POPULATION A POPULATION BNeutralismCommensalismSynergismMutualismCompetitionAmensalismParasitismPredation 0 0 +-0 or+0 +-9.3 Biogeochemical cycles1.Carbon cycle2.Nitrogen cycle3.Sulfur cycle4.Iron cycleCarbon cycleCarbon cycleCarbon dioxide is incorporated,or fixed,into organic comp
17、ounds by such photoautotrophs as cyanobacteria,green plants,algae,and green and purple sulfur bacteria.Chemoheterotrophs consume the organic compounds,animals eat photoautotrophs,especially green plants,and may in turn be eaten by other animals.When the organisms die,the organic compounds of their b
18、odies are deposited in the soil and are decomposed by microorganisms,principally by bacteria and fungi.During this decomposition,carbon dioxide is returned to the atmosphere.Nitrogen cycleProteins fromdead cells andwaste products MicrobialdecompositionAmino acidsAmino acidsAmmonia(NH3)ammonification
19、Almost all the nitrogen in the soil exists in organic molecules,primarily in proteins.When an organism dies,the process of microbial decomposition results in the hydrolytic breakdown of proteins into amino acids.The amino groups of amino acids are removed and converted into ammonia(NH3).Ammonificati
20、on is brought about by numerous bacteria and fungi.NH4+N02-NitrosomonasAmmonium ionNitrite ionN02-N03-Nitrite ionNitrate ionNitrobacterNitrification involves the oxidation of the ammonium ion to nitrateThe genera Nitrosomonas and Nitrobacter are autotrophic nitrifying bacteria.These organisms obtain
21、 energy by oxidizing ammonia or nitrite.In the first stage,Nitrosomonas oxidizes ammonium to nitrites.In the second stage,such organisms as Nitrobacter oxidize nitrites to nitrates Key processes and prokaryotes in the nitrogen cycle Processes Example organismsNitrification(NH4+NO3-)NH4+NO2-Nitrosomo
22、nas NO2-NO3-NitrobacterDenitrification(NO3-N2)Bacillus,Pseudomonas N2 Fixation(N2+8H NH3+H2)Free-living Aerobic Azotobacter Cyanobacteria Anaerobic Clostridium,purple green bacteria Symbiotic Rhizobium Bradyrhizobium.FrankiaAmmonification(organic-N NH4+)Many organisms can do thisSulfur cycleKey proc
23、esses and prokaryotes in the sulfur cycleProcesses OrganismsSulfide/sulfur oxidation(H2SS0 SO42-)Aerobic Sulfur chemolithotrophs (Thiobacillus,Beggiatoa,many others)Anaerobic Purple and green phototrophic bacteria,some chemolithotrophsSulfate reduction(anaerobic)(SO42-H2S)Desulfovibrio,Desulfobacter
24、Sulfur reduction(anaerobic)(S0 H2S)Desulfuromonas,many hyperthermophilic ArchaeaSulfur disproportionation(S2O32-H2S+SO42-)Desulfovibrio and othersOrganic sulfur compound oxidation or reduction(CH3SHCO2+H2S)(DMSODMS)Desulfurylation(organic-S H2S)Many organisms can do this9.4 Plant-microbe interaction
25、s1.Lichens and Mycorrhizas2.The plant environment3.Root nodule bacteria and symbiosis with legumesLichensLichens are leafy or encrusting growths that are widespread in nature and are often found growing on bare rocks,tree trunks,house roofs,and surfaces of bare soils.The lichen plant consists of a s
26、ymbiosis of two organisms,a fungus and an alga.Lichens consist of a tight association of many fungal cells within which the algal cells are embedded.MycorrhizasMycorrhiza literally means root fungus and refers to the symbiotic association that exists between plant roots and fungi.Probably the roots
27、of the majority of terrestrial plants are mycorrhizal.There are two classes of mycorrhizae:ectomycorrhizae,in which fungal cells form an extensive sheath around the outside of the root with only little penetration into the root tissue itself,and endomycorrhizae,in which the fungal mycelium is embedd
28、ed within the root tissue.Mycorrhizas Type of Mycorrhizas:Ectomycorrhiza and EndomycorrhizaMorphology and Function of Mycorrhizal InfectionMycorrhiza and Plant NutritionApplication Potential of VAM in Agricultural practice and EcosystemDevelopment and Application of Molecular Probes Construction and
29、 Analysis of Genomic Library MycorrhizasEctomycorrhizasEndomycorrhizasEctendomycorrhizasFunctions of mycorrhizaRoot Nodule Bacteria and Symbiosis with LegumesRoot Nodule Bacteria and Symbiosis with Legumes Stages in Nodule FormationBiochemistry of Nitrogen Fixation in NodulesGenetics of Nodule Forma
30、tion:nod GenesGenetic Cooperativity in the Rhizobium-legume SymbiosisConstruction and Application of Genetic-engineered Rhizobium Symbiosis of Frankia and Non-leguminous PlantSymbiosis of Frankia and Non-leguminous Plant Morphology and Physiological Characteristic of FrankiaHostsApplication Potentia
31、l 8.5 Bioremediation1.Pollutants2.Means of bioremediationPollutants1,Microorganisms are an important part of ecosystems 2,Microbial communities are complex 3,Microbial growth requires nutrients and all of which must be present in usable forms4,Most microorganisms normally associated with higher orga
32、nisms and those grown in the lab.tend to be less able to compete and survive in soils and waters5,Extreme environments restrict the range of microbial types which are able to survive and functionConceptsMicroorganisms in NatureDistribution of microorganisms In:SoilWaterAirFoodWith plants and animals
33、Proportion of different soil microorganisms in soilAgrobacteriumAlcaligenesArthrobacterBacillusCaulobacterCellulomonasClostridiumCorynebacteriumFlavobacteriumMicrococcusMycobacteriumPseudomonasStaphylcoccusMain types of soil microorganismsMicrobial number and biomass in cultivated field soil（15 cm）M
34、icrobesNumbers/gramBiomass（g/m3）Bacteria108160Fungi105200Actinomycetes105-106160Algae104-10532Protozoa10438The rhizosphere is the soil region in close contact with plant roots.Within the rhizosphere,the plant roots exert a direct influence on the soil bacteria.This influence is known as the rhizosph
35、ere effect.In the rhizosphere,microbial populations reach much higher densities in the rhizosphere than in the free soil.Rhizosphere Effect R/SMicrobial populations in the rhizosphere may benefit the plant by:(1)removing hydrogen sulfide,which is toxic to the plant roots(2)increasing solubilization of mineral nutrients needed by the plant for growth(3)(3)synthesizing vitamins,amino acids,auxins,gibberellins that stimulate plant growth(4)(4)antagonizing potential plant pathogens through competition and the production of antibiotics Microorganisms in water and air