This study was conducted to evaluate the effects of Bacillus subtilis SC02 supplement on water quality, microbial community diversity and structure in a grass carp (Ctenopharyngodon idellus) culture. Our selected strain, B. subtilis SC02, significantly reduced ammonia, nitrite and total nitrogen levels in water over an extended period compared with the control group. Pyrosequencing showed that the Shannon diversity index (Shannon) and species richness estimators (Chao) of the treatment group were higher, indicating that bacterial richness was significantly increased in the treatment group. The phyla Proteobacteria, Bacteroidetes and Actinobacteria were dominant in the treatment groups, accounting for 45, 21.9 and 21.9 % of the sequence reads, respectively. However, in sharp contrast, the control fishes were predominantly occupied by Proteobacteria (82.1 %) and Firmicutes (8.4 %). At the genus level, the microbial communities were different between the control and treatment groups, although the two groups shared similar genera. Additionally, some genera (such as Tepidimonas, Variovorax, Roseomonas, Rubritepida, Nitrobacter, etc.) only appeared in the treatment group, and many other genera only existed in the control group. Therefore, we conclude that the addition of the SC02 strain in water improves water quality, which may ultimately be a result of changes in microbial community diversity in grass carp cultures.

To reduce ammonium and nitrite in aquaculture water, an isolate of the denitrifying bacterium Pseudomonas stutzeri, SC221-M, was obtained. The effects of various nitrogen and carbon sources, the ratio of carbon to nitrogen and temperature on bacterial growth, denitrification rates and the expression levels of nirS and nosZ in SC221-M were studied. The following conditions were determined to be optimal for growth and denitrification in SC221-M: NaNO2 as the nitrogen source, sodium citrate as the carbon source, a carbon to nitrogen ratio range of 4–8, and a temperature range of 20–35°C. Subsequently, SC221-M and the Bacillus cereus BSC24 strain were selected to generate microbial preparations. The results showed that addition of the microbial preparations decreased various hydrochemical parameters, including total dissolved solids, ammonium, nitrite, total nitrogen and the chemical oxygen demand. Nitrogen removal rates were highest on day 9; the removal rates of BSC24, SC221-M, a mixed preparation and a 3× mixed preparation were 24.5%, 26.6%, 53.9% and 53.4%, respectively. The mixed preparation (SC221-M+BSC24) was more effective at removing nitrogen than either the SC221-M or BSC24 preparation. Roche 454 pyrosequencing and subsequent analysis indicated that the control and other groups formed separate clusters, and the microbial community structure in the water changed significantly after the addition of microbial preparations. These results indicate that the addition of microbial preparations can improve both the water quality and microbial community structure in an experimental aquaculture system. P. stutzeri strain SC221-M and its related microbial preparations are potential candidates for the regulation of water quality in commercial aquaculture systems.

No abstract

This experiment was conducted to study the effect of dietary supplementation of probiotic on performance and intestinal microflora of Chinese soft-shelled turtle. Healthy Chinese soft-shelled turtles (6000 pieces with average weight of 5 g) were selected and randomly divided into two groups: control and treatment with three replicates each. The control was fed on normal basal diet, whereas treatment was fed on basal diet supplemented with 1 9 10 8 cfu.g À1 Bacillus subtilis preparation. The results showed that the final mean weight of treatment (265.84 AE 3.48 g) was significantly higher (P < 0.05) than that of control (240.45 AE 4.32 g). There was significant difference (P < 0.05) in FCR, and DGs were obtained in probiotics fed group as compared to control. The level of sucrase, maltase, amylase, lipase and ATPase of treatment was significantly higher (P < 0.05) than that of control. Pyrosequencing showed that the dietary supplementation of probiotic Bacillus strain decreased microbial diversity. Phylum Firmicutes was dominant in both groups. Compared with the control, Firmicutes was increased, while others were decreased in treatment group. The results indicated that dietary supplementation of probiotic can improve growth performance, digestibility and intestinal microflora in Chinese soft-shelled turtle.