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1、Chapter 9 Microbial Ecology,Microbial ecology=?Environmental microbiology,The 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 environ
2、ments.,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
3、presence and activities.,9.1 Microorganisms in nature ecosystem,9.2 Microbial population interactions,9.3 Biogeochemical cycles,9.4 Plant-microbe interactions,9.5 Bioremediation,Chapter 9 Microbial Ecology,9.1 Microorganisms in nature ecosystem,1.Microorganisms and microenvironment2.Terrestrial Envi
4、ronments3.Freshwater Environments4.Marine Environments,9.1.1 Microorganisms and microenvironment,populations,guilds,communities,ecosystem,Metabolically related populations constitute groupings called guilds.,Sets of guilds conducting complementary physiological processes interact to form microbial c
5、ommunities.,In a microbial ecosystem individual cells grow to form populations.,Community 3,Microbial 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 o
6、n the growth conditions.,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
7、 distance away,can remain 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 Enviro
8、nments,Proportion of different soil microorganisms in soil,Microbial number and biomass in cultivated field soil（15 cm）,Main types of soil microorganisms,The rhizosphere is the soil region in close contact with plant roots.,Within the rhizosphere,the plant roots exert a direct influence on the soil
9、bacteria.This influence is known as the rhizosphere effect.,In the rhizosphere,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 roots(2)increasing solubilization of miner
10、al nutrients needed by the plant for growth(3)synthesizing vitamins,amino acids,auxins,gibberellins that stimulate plant growth(4)antagonizing potential plant pathogens through competition and the production of antibiotics,Microbial populations in the rhizosphere may benefit the plant by:,1，neutrali
11、sm(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),9.2 Microbial population interactions,Neutralism,there is no any physiological effect between the populations.,Commensalism is a unidirectional relationship between
12、 populations in which one population benefits and the other one 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 interrelationshipb
13、etween two populations that benefits both ofthem.Lichens is composed 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.,Parasitis
14、m,the parasite population is benefited and the host population is harmed.,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 interaction,0,N
15、o effect;+,positive effect;-,negative effect.,9.3 Biogeochemical cycles,1.Carbon cycle2.Nitrogen cycle3.Sulfur cycle4.Iron cycle,Carbon cycle,Carbon cycle,Carbon dioxide is incorporated,or fixed,into organic compounds by such photoautotrophs as cyanobacteria,green plants,algae,and green and purple s
16、ulfur 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 bodies are deposited in the soil and are decomposed by microorganisms,principally by ba
17、cteria and fungi.During this decomposition,carbon dioxide is returned to the atmosphere.,Nitrogen cycle,Proteins fromdead cells andwaste products,Microbialdecomposition,Amino acids,Amino acids,Ammonia(NH3),ammonification,Almost all the nitrogen in the soil exists in organic molecules,primarily in pr
18、oteins.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).Ammonification is brought about by numerous bacteria and fungi.,NH4+,N02-,Nitrosomonas,Amm
19、onium ion,Nitrite ion,N02-,N03-,Nitrite ion,Nitrate ion,Nitrobacter,Nitrification involves the oxidation of the ammonium ion to nitrate,The genera Nitrosomonas and Nitrobacter are autotrophic nitrifying bacteria.These organisms obtain energy by oxidizing ammonia or nitrite.In the first stage,Nitroso
20、monas oxidizes ammonium to nitrites.In the second stage,such organisms as Nitrobacter oxidize nitrites to nitrates,Key processes and prokaryotes in the nitrogen cycle,Sulfur cycle,Key processes and prokaryotes in the sulfur cycle,9.4 Plant-microbe interactions,1.Lichens and Mycorrhizas2.The plant en
21、vironment3.Root nodule bacteria and symbiosis with legumes,Lichens,Lichens 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 symbiosis of two organisms,a fungus and
22、 an alga.Lichens consist of a tight association of many fungal cells within which the algal cells are embedded.,Mycorrhizas,Mycorrhiza literally means root fungus and refers to the symbiotic association that exists between plant roots and fungi.Probably the roots of the majority of terrestrial plant
23、s 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 embedded within the root tissue.,Mycorrhiz
24、as,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 Analysis of Genomic Library,Mycorr
25、hizas,EctomycorrhizasEndomycorrhizasEctendomycorrhizas,Functions of mycorrhiza,Root Nodule Bacteria and Symbiosis with Legumes,Stages in Nodule FormationBiochemistry of Nitrogen Fixation in NodulesGenetics of Nodule Formation:nod GenesGenetic Cooperativity in the Rhizobium-legume SymbiosisConstructi
26、on and Application of Genetic-engineered Rhizobium,Symbiosis of Frankia and Non-leguminous Plant,Morphology and Physiological Characteristic of FrankiaHostsApplication Potential,8.5 Bioremediation,1.Pollutants2.Means of bioremediation,Pollutants,1,Microorganisms are an important part of ecosystems 2
27、,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 organisms and those grown in the lab.tend to be less able to compete and survive in soils and waters5,Extreme environments re
28、strict the range of microbial types which are able to survive and function,Concepts,Microorganisms in Nature,Distribution of microorganisms In:SoilWaterAirFoodWith plants and animals,Proportion of different soil microorganisms in soil,Main types of soil microorganisms,Microbial number and biomass in
29、 cultivated field soil（15 cm）,The 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 rhizosphere,microbial populations reach much higher densi
30、ties in the rhizosphere than in the free soil.,Rhizosphere Effect R/S,Microbial populations in the rhizosphere may benefit the plant by:removing hydrogen sulfide,which is toxic to the plant rootsincreasing solubilization of mineral nutrients needed by the plant for growth(3)synthesizing vitamins,amino acids,auxins,gibberellins that stimulate plant growth(4)antagonizing potential plant pathogens through competition and the production of antibiotics,Microorganisms in water and air,
