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 envi
2、ronments.,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
3、microbial 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 microenvironment 2. Ter
4、restrial Environments 3. Freshwater Environments 4. 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
5、 form microbial communities.,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 (nutrien
6、ts) available and on 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
7、 center, only a very short 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 parti
8、cles.,9.1.2. Terrestrial Environments,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
9、 a direct influence on the soil 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 root
10、s (2) increasing 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,Microbial populations in the r
11、hizosphere 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， 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
12、 between the populations.,Commensalism is a unidirectional relationship between 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
13、 surviving independently.,Mutualism Symbiosis is an obligatory interrelationship between two populations that benefits both of them. 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
14、when one population produces a substrate inhibitory to another population.,Parasitism, 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 thi
15、s normal results in the death of the prey.,Classification of population interaction,0, No effect; +, positive effect; -, negative effect.,9.3 Biogeochemical cycles,1. Carbon cycle 2. Nitrogen cycle 3. Sulfur cycle 4. Iron cycle,Carbon cycle,Carbon cycle,Carbon dioxide is incorporated, or fixed, into
16、 organic compounds 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 organi
17、c compounds of their bodies 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 cycle,Proteins from dead cells and waste products,Microbial decomposition,Amino acids,Amino
18、 acids,Ammonia (NH3),ammonification,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
19、converted into ammonia (NH3). Ammonification is brought about by numerous bacteria and fungi.,NH4+,N02-,Nitrosomonas,Ammonium 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
20、autotrophic nitrifying bacteria. These organisms obtain 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,Sulfur c
21、ycle,Key processes and prokaryotes in the sulfur cycle,9.4 Plant-microbe interactions,1. Lichens and Mycorrhizas 2.The plant environment 3. 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 bar
22、e rocks, tree trunks, house roofs, and surfaces of bare soils . The lichen plant consists of a symbiosis 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 .,Mycorrhizas,Mycorrhiza literally means “root fungus
23、“ and refers to the symbiotic association that exists between plant roots and fungi. Probably the roots 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 onl
24、y little penetration into the root tissue itself, and endomycorrhizae, in which the fungal mycelium is embedded within the root tissue.,Mycorrhizas,Type of Mycorrhizas: Ectomycorrhiza and Endomycorrhiza Morphology and Function of Mycorrhizal Infection Mycorrhiza and Plant Nutrition Application Poten
25、tial of VAM in Agricultural practice and Ecosystem Development and Application of Molecular Probes Construction and Analysis of Genomic Library,Mycorrhizas,Ectomycorrhizas Endomycorrhizas Ectendomycorrhizas,Functions of mycorrhiza,Root Nodule Bacteria and Symbiosis with Legumes,Stages in Nodule Form
26、ation Biochemistry of Nitrogen Fixation in Nodules Genetics of Nodule Formation: nod Genes Genetic Cooperativity in the Rhizobium-legume Symbiosis Construction and Application of Genetic-engineered Rhizobium,Symbiosis of Frankia and Non-leguminous Plant,Morphology and Physiological Characteristic of
27、 Frankia Hosts Application Potential,8.5 Bioremediation,1. Pollutants 2. Means of bioremediation,Pollutants,1, 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 forms 4, Most micro
28、organisms normally associated with higher organisms and those grown in the lab. tend to be less able to compete and survive in soils and waters 5, Extreme environments restrict the range of microbial types which are able to survive and function,Concepts,Microorganisms in Nature,Distribution of micro
29、organisms In: Soil Water Air Food With plants and animals,Proportion of different soil microorganisms in soil,Main types of soil microorganisms,Microbial number and biomass in cultivated field soil（15 cm）,The rhizosphere is the soil region in close contact with plant roots.,Within the rhizosphere, t
30、he 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 densities in the rhizosphere than in the free soil.,Rhizosphere EffectR/S,Microbial populations in the rhizosphere may benefit
31、the plant by: removing hydrogen sulfide, which is toxic to the plant roots increasing 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,
