Analysis Of NifH、amoA、nirK、nosZ Gene Diversity In Waterbody Of Rice Floating-Bed

As the third-largest freshwater lake in China, eutrophication in Taihu Lake is deepening the destruction of ecosystem, seriously affecting the sustainable development of agriculture and environment of the region. We can evaluate the water quality from three aspects:physical indicators, chemical indicators and biological indicators. Water micro-organisms have an important impact on the water quality as indicators of water quality. But we lack the data about changes in the community structure Rice floating-bed impact on functional microbial of the water bodies and the research in this area will provide some scientific basis in the causes and governance about the Eutrophication.Nitrogen is the main elements to generate the problem of water eutrophication, and functional microbial relate to the nitrogen removal solve the problem of the eutrophication as a key factor in the water bodies, including nitrogen-fixing microorganisms, ammonia-oxidizing bacteria and denitrifying bacteria. Most of microbial species is difficult to cultivate under the experimental conditions, bypassing the difficulties of traditional microbial isolation and culture we can use these molecular biological techniques and become the trend of the study of microbial diversity. The subject chosen ecological base of rice floating bed in the town of hudai, studying the impaction on the functional genes diversity (of nifH, amoA, nirK.nosZ) of nitrogen-fixing microbes, ammonia-oxidizing bacteria, denitrifying bacteria by molecular biology methods of RFLP (Restriction Fragment Length Polymorphism).For the nifH gene of nitrogen-fixing microorganisms, we obtained176clones and30RFLP in the three gene libraries,52positive clones and18different RFLP band types in nifH-LW library;71positive clones and8different types in nifH-FW library;53positive clones and19different types in nifH-RW library; The diversity indexes of nifH-RW library is higher than others,nifH-FW has a lower diversity indexes and large difference with nifH-RW and nifH-LW library. The diversity indexes of nitrogen-fixing microorganisms are reduced in the order of RW sample, LW sample, FW sample. According to the sequencing results, most clones have a high similarity with the known nitrogen-fixing microorganisms in Proteobacteria.We obtained183clones and20RFLP in the three amoA gene libraries.66positive clones and9different types in amoA-LW library;55positive clones and10different types in amoA-FW library;62positive clones and12different types in amoA-RW library. The diversity indexes of amoA gene libraries is lower and similar with each other. The diversity indexes of amoA gene libraries are reduced in the order of RW sample, FW sample, LW sample. amoA-FW and amoA-LW librariy have the same dominant type and the similarity with Nitrosomonas sp. is98%and99%respectively. The similarity of Nitrosovibrio sp. and dominant type of amoA-RW librariy is94%.We obtained174clones and53RFLP in the three nosZ gene libraries.50positive clones and27different RFLP band types in nosZ-LW library;63positive clones and28different types in nosZ-FW library;61positive clones and38different types in nosZ-RW library. The diversity indexes of nosZ gene libraries are reduced in the order of RW sample, LW sample, FW sample.The dominant type of nosZ-FW has a high similarity with uncultured bacteria, The similarity of the dominant type of nosZ-LW with Pseudomonas sp is92%,and the dominant type of nosZ-RW is88%with Azospirillum sp.And we obtained223clones and61RFLP in the three nirK gene libraries.80positive clones and31different RFLP band types in nirK-LW library;75positive clones and36different types in nirK-FW library;68positive clones and35different RFLP band types in nirK-RW library. The diversity indexes of nirK gene libraries are reduced in the order of FW sample.RW sample,LW sample.The dominant type of nirK-LW has a high similarity with Ochrobactrum sp of99%,and the dominant type of nirK-RW and nirK-FW has a high similarity with uncultured bacteriaThe study of microbial genetic diversity about nitrogen metabolism showed that rice floating-bed system can significantly change the number and types of bacteria in water, we suggest that the introduction of rice floating-bed make a large change in the dominant flora and structure of the microbial community in the water and promote the nitrogen cycle of waterbody and enhance the self-purification of waterbody. The results lay the theoretical foundation for treatment of the eutrophic water taking advantage of the terrestrial plants floating bed and provide a scientific basis for the development of ecological floating-bed.