Bacterial Community Structure Of Rice Floating-Beds Waters And Isolation Of Aerobic Denitrifying Bacterium

The water eutrophication is increasingly serious harm to social and economic development, environmental protection and human health, which has become a worldwide environmental issue of water and has been concerned by every country. Eutrophication is mainly caused by higher levels of nitrogen, phosphorus and other nutrition for algae use in water. Ecological floating-beds is capable of absorbing N, P and other elements in water by plant roots degrading other harmful pollutants. It not only purifies and protects aquatic environment, but also brings a certain economic benefits. Ecological floating-beds technology as one of biological methods has been used by more and more people to treat eutrophic water. Rice is an important food crop, which can be planted on ecological floating-beds. It not only can control water pollution, but also bring considerable social and economic benefits. But the studies on changes of microbial community structure and the mechanism of nitrogen and phosphorus removal caused by rice floating-beds don’t go far enough.Bacterial community structure of floating-beds rice roots, water nearest the roots, water nearest floating-beds area, water far away from floating-beds area, Long Yan river water near experimental waters with floating-beds were studied by using DGGE fingerprinting technique during rice tillering stage of the floating-beds rice. The results of testing the number of bacteria and nitrogen, phosphorus content show that the number of bacteria in water is about10cfu/ml, and the bacteria number in water processing with rice floating-beds is lower than in Long Yan river, and there are a lot of bacteria in roots of rice, reaching about108cfu/g; the bacterial community structure of each sample is different, dominant population has changed significantly; the rice floating-beds can already purify water body at tillering stage; the rice floating-beds can already purify water body at tillering stage, making the different forms of nitrogen and phosphorus in water decreased significantly, especially decreasing ammonia nitrogen and total phosphorus, but the ammonia nitrogen in water nearest the roots is relatively high even more than heavily polluted Long Yan river, this may be related to the adsorption, flocculation, secretion of organic of the roots and lots of bacteria around the roots which can fix and transform nitrogen.Bacterial community structure of water nearest the floating-beds rice roots, water far away floating-beds area, Long Yan river water were studied by using both DGGE and RFLP fingerprinting technique during rice tillering stage of the floating-beds rice. The results show that three waters all have a high bacterial diversity. The diversity of water nearest the roots is lower than water far away from floating-beds area and Long Yan river water, and also has the different dominant population. The results of the two methods show that:the dominant bacterial populations of water nearest the floating-beds rice roots are Sphingobacteriales, Burkholderiales, Rhizobiales, Actinomycetales; the dominant bacterial populations of water far away from floating-beds area are Rickettsiales, Actinomycetales, Sphingobacteriales, Rhizobiales, Acidimicrobiales and Burkholderiales; the dominant bacterial populations of Long Yan river water are Actinomycetales, Planctomycetales, Methylophilales and Rhizobiales. These dominant bacterial populations have the role of Nitrogen fixation, nitrification, denitrification, dephosphorization, cellulose and organic matter degradation, absorption metal ions, production bioflocculant, etc, and can purify water in different ways.The aerobic denitrifying bacteria were isolated from rice floating-beds treated water with traditional isolation and culture methods. A fast and simple method of screening aerobic denitrifiers was established.7strains of aerobic denitrifying bacteria which have efficient denitrification in anoxic and aerobic conditions were screened. They belong to Pseudomonas, Ochrobactrum, Brevundimonas, Microbacterium. With initial nitrate nitrogen concentration of150mg/L, the best two Pseudomonas strains’s removal rate of nitrate can reach more than95%within55hours and there is no nitrite excessive accumulation. The studies on their physiological and biochemical characteristics and optimum culture condition offer some useful information for practical application.