[Analysis of Microbial Diversity in a Fluidized-Sand Biofilter Based on High-Throughput Sequencing Technology].

In order to understand the microbial community composition and mechanism of purifying aquaculture water with a biofilter that was been applied to spotted parrotfish recirculating aquaculture systems with microglass beads as the biofilter filler, the changes in the nutrients of different biological filter beds and the water treatment performance of a fluidized-sand biofilter were analyzed. By using high-throughput sequencing technology, the microbial community structure of the surface area and bottom area at different times were studied. The results show that the fluidized-sand biofilter successfully start-up after one month under marine culture. Nitrification of the biofilter occurred mainly in the lower bed layer; the surface area played a small role in eliminating the NH4+-N. The average removal rates of NH4+-N, TN, BOD5, and SS were 68.3%±2.24%, 49.54%±3.56%, 60.35%±4.98%, and 45.21%±2.11%, respectively. The average NH4+-N removal load reached (343.28±75.5) g·(m3·d)-1, which showed a better performance of wastewater treatment. In this experiment, 31 phyla and 490 genera were identified, thus the biological diversity was significantly higher than that of the other conventional microbial biofilter. Start-stop cycling of the self-cleaning device in the biofilter had no effect on the microbial diversity of different regional, but had some effect on the dominant bacterial community of the microglass beads surface. Under opening self-cleaning device regularly condition, the microbial species of the surface and bottom areas became significantly similar. With time, the microbial species of the superficial area and bottom area had no significant change, and the microbial population structure was relatively stable. In the biofilm training period, the diversity of microbial communities was significantly lower than it was after biofilm maturation. At the time of biofilter stable operation, the dominant bacteria of the superficial zone essentially remained unchanged and mainly included Anaerolineaceae_uncultured (8.4%-28%), Flavobacteriaceae_unclassified (1.1%-32%), Rhodobacteraceae_uncultured (2.3%-17%), Nitrospira(1%-7%), and Caldilineaceae_uncultured (1%-6%). The dominant bacteria of the bottom zone changed over time and mainly include Nitrospira (12.45%-17.06%), Candidatus_Microthrix (2.6%-8.8%), Muricauda (4.8%-6.3%), Defluviimonas (6%-7%), and Rhodobacteraceae_uncultured (2%-6.2%). Among them, the abundance of Nitrospira was significantly higher than that in the other biofilter.

[Analysis of the changes of microbial community structure on bio-carrier of recirculating aquaculture systems (RAS)].

In order to study the variation of microbial community structure and the mechanism of denitrification on bio-carrier in recirculating aquaculture systems (RAS) during the periods of bio-film formation and operation the systems, traditional microbiological methods were applied to count the quantity of heterotrophic bacteria, ammonia oxidize bacteria and nitrite oxidize bacteria. The amplified products of variable V3 region of bacterial 16S rDNA were separated by using denaturing gradient gel electrophoresis (DGGE). And bacterial community DNA fingerprint was obtained. The sequences retrieved from the DGGE bands were used for homology analysis and construction of phylogenetic tree. It presented a trend that the quantity of the three types of bacteria increased gradually to a top and then fallen slowly to a stable level. The composition of microbial community of bio-carrier was very abundant in all periods, and the Shannon index was 1.53, 1.44, 1.57, 1.08, 1.27 and 1.30, respectively. During different periods, there was a certain shift in the microbial community structure, while the C(s) value (similar index) in two adjacent periods was high, indicating the variation and succession of the microbial community was slow and regular. Several bacteria had an effect on removal of pollutants for farming water and the effluent water quality could meet the requirements of high-density culture. Among them, Proteobacteria and Flavobacteria were main communities. The Nitrosomonas and some other facultative anaerobic bacteria (Flavobacteriaceae bacterium) were identified, which indicated that there may be coexisted pathways of nitrification and denitrification in bio-filter.