| Portunus trituberculatus and Litopenaeus vannamei have become two major economic aquaculture species in China due to their rapid growth, and profitable farming. Although their culture can take the advantage of time and space ecosystem and improve the utilization of food, they can also result in the accumulation of ammonia and other harmful substances which may destroy the aquatic environment. Bio-floc technology as a new biological technique not only is used to improve water environment, the animal survival rate and feed utilization, but also can promote the growth of bacteria and so on. Therefore, an increasing attention is being paid to their application in aquaculture system. Bacteria, as part of the microbial ecosystem components, play a very important role in the material circulation and energy flow, as well as in maintaining stable environments and preventing the diseases. Accordingly, it is very significant to study microbial community composition and function. In this study, biological floe technology was applied in analyzing bacterial productivity and community structure of the polyculture system of P. trituberculatus and L. vannamei. What’s more, changes of the number of heterotrophic bacteria and Vibrio and the functional diversity of the bacterial community were also analyzed by adding different probiotics to the farming systems. In terms of microbiology, the regulation of bacteria and carbon sources could be a useful means to improve aquatic environments to promote the growth of P. trituberculatus and L. vannamei in the polyculture system. The main results were listed as following:1. Effects of C/N levels on bacterial productivity in the polyculture system of P. trituberculatus and L. vannameiEffects of C/N levels Bacterial productivity (BP) in P. trituberculatus and L. polyculture system were studied in situ using land-based enclosures. During the experiment, all groups to which molasses were added, except C4 group, showed a trend of increasing continuously with time elapsed, while the control group (CO) reached the minimum value in August. The different groups ranged from (208.67±8.50)～(821±13.00) μgC/(L.d) with the average of 439.53 μgC/ (Ld). At the beginning, no significant difference was observed in BP among different treatments, while at the middle, the experimental groups were significantly higher than control group (P< 0.05), with the higher value being observed in C2 and C3 group (P<0.05). According to RDA analysis, changes in Bacterial productivity (BP) and bacterial number (BN) were the synergistic result of multi abiotic factors of which the major were NH+-N、NO2--N, NO3--NU TOC and Chi a in July, NH4+-N、 N02--N、NO3-N. TN and TP in August and NH+-N、NO2--N、NO3-N and PO4--P in September.2. Effects of C/N levels on microbial community structure in the polyculture system of P. trituberculatus and L. vannameiIn the present study, the PCR-DGGE (denaturing gradient gel electrophoresis) technology, redundancy analysis (RDA) and the diversity index were employed to characterize the bacterial community structure in the polyculture system of P. tritiberculatus and L. vannamei to investigate the effects of abiotic factors. Four other C/N levels (i.e.10,15,20 and 25) were set in this experiment by the addition of molasses into artificial feed, and the four treatments were represented by C1, C2, C3 and C4 group respectively. The group treated with basic feed was used as control. Results from this study demonstrated the major bacteria of Actinobacteria, Cyanobacteria, Proteobacteria (α,β, γ,δ andε), Bacteroidetes and Bacillibacteria in seawater of this polyculture system. A similar bacterial community structure was obtained between treatments of C1, C2, C3 and C4, all being significantly different from CO group. All groups had a similar dominant bacterial community, with Actinobacteria being dominant all over aquaculture activity, while there was a significant difference between treatments in the relative amount of dominant bacterial community. In comparison with control, the microbial community diversity increased with the aquaculture time. Rather than control group, y-Proteobacteria was detected in August in other treatments and ε-Proteobacteria and Bacillibacteria in September. The diversity index showed a variation trend of increasing first and then decreasing and reached the maximum in August. No significant change of Pielou index was observed among all treatments, while Shannon-Wiener index increased first and then decreased, being highest in C2 group and lowest in C4 group in September. According RDA analysis, the changes in microbial community structure was the synergistic result of multi abiotic factors of which the major were TOC> TN> NO3--N> TP> PO4--P> NH4+-N in July, TP> NH4+-N> NO2--N> PO4--P in August and NO2-N> NO3-N> PO4--P> NH/-N> pH> TN> TOC in September. The preliminary experimental results showed that the C/N level of 15 was better for the polyculture system of P. trituberculatus and L. vannamei in seawater purification and in maintenance of the microbial community structure.3.Effect of carbon source on microbial community functional diversity in the polyculture system of P. trituberculatus and L. vannameiTraditional culture method was used to study the change of the number of heterotrophic bacteria and vibrio. Biolog method was used to analyze the functional diversity of water microbial communities in the polyculture system of P. trituberculatus and L. vannamei which were controlled by probiotics and carbon source. In this experiment, six treatments, i.e. four experimental treatments represented by C2 (bacillus pumilus), C3 (bacillus cereus), C4 (nitrobacteria) and C5 (EM) group respectively to which bacteria and molasses were added, one negative control treatment named C1 to which only molasses were added and one blank control treatment named CO to which no bacteria or molasses were conducted, were set. Results show that the amounts of heterotrophic bacteria, Vibrio in water and sediment changed greatly during the cultural period. On the time scale, the amounts of all heterotrophic bacteria showed the same trend of increasing at the beginning and then decreasing, while the amount of vibrio kept increasing. C3 and C4 groups were similar in the number of heterotrophic bacteria, with both significantly higher than C4 and CO. The number of vibrio in CO group was higher than carbon added groups. Biolog-ECO examination showed that a significance was observed among different treatments in the number of carbon substrate utilization and the use of strength. In the later stage of the experiment, metabolic activity and the six carbon source utilization of the microbial communities in C3 were significantly higher than the other treatments during the entire breeding while C4 and CO reached the lowest value (P< 0.05). PCA analysis showed that bacterial communities in different treatments show changing trends and microbial community functional diversity of C3 and C4 treatments were significantly different to the other treatments throughout the experiment. However, compared to the other treatments, diversity indexes of microbial communities of C3 was significantly higher and C4 was significantly lower (P<0.05)... |
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