生物絮团培养过程中养殖水体水质因子及原核与真核微生物的动态变化

在草鱼(Ctenopharyngodon idella)养殖系统中维持碳氮比为20︰1、水温(26.0±2.3)℃、pH7.2~7.8, 24 h不间断供氧以形成生物絮团, 监测培养过程中养殖水体总氮(TN)、总固体悬浮物(TSS)浓度、碱度的动态变化及分析生物絮团的营养组分, 并应用PCR-DGGE技术研究生物絮团的原核及真核微生物组成和动态变化。养殖水体TN变化范围为6.65~11.15 mg/L, 第9天达到峰值(10.11±1.05) mg/L, 第12天后和第0天时的TN水平无显著性差异(P>0.05); TSS浓度在第9天达到最大值(419.67±11.5) mg/L, 第15天后TSS稳定维持在244.67 mg/L; 碱度变化范围为136.68~239.20 mg CaCO₃/L, 第 6天达到峰值后逐渐下降并趋于平稳。生物絮团的粗蛋白含量为30%(干重)。生物絮团原核微生物主要由变形菌门(Proteobacterium)、放线菌门(Actinobacteria)、拟杆菌门(Bacteroidetes)和某些未知不可培养的细菌组成, 蓝细菌(Cyanobacterium)只存在于生物絮团培养前期(第0、5、10天), 产碱菌科细菌(Alcaligenaceae)存在于生物絮团形成的整个过程, 且是第5、10、15天的优势菌。组成生物絮团的真核微生物隶属于原生动物门的斜叶虫属(Loxophyllum)、隐藻纲的隐鞭藻科(Cryptomonadaceae)及Goniomonas属、硅藻纲的双头菱形藻属(Nitzschia)。其中双头菱形藻属为絮团培养初始第0天到15天特有; 斜叶虫属在絮团培养后期分布较多。结论认为, 生物絮团系统在养殖的15 d左右达到稳定运行的状态, 能有效调节养殖系统菌藻分布, 控制养殖水质, 维持整个系统的平衡与良性发展。

Dynamic changes of water quality factors and composition of prokaryotic and eukaryotic microorganisms during culturing of bio-floc

A 30-day experiment was conducted to investigate the effectiveness of bio-floc technology for maintaining good water quality in Ctenopharyngodon idellus with average weight of (121.61±14.23) g farming ponds. The total suspended solids(TSS), total nitrogen (TN) and alkalinity (CaCO₃) were determined every 3 days and microbial communities of the bio-floc were analyzed using the PCR-DGGE (PCR-denaturing gradient gel electrophoresis) every 5 days, respectively. The results showed that water TSS concentration reached a peak value of (419.67±11.5) mg/L on the 9th day, which was significantly (P<0.05) higher than that of the other time points. From the 15th day on, the TSS remained at a relatively stable level of 244.67 mg/L. The TN ranged from 6.65 to 11.15 mg/L, and it reached the peak value of (10.11±1.05) mg/L on the 9th day. There was no significant difference in TN between water after the 12th day and water at the beginning of the farming trial (P>0.05). Alkalinity in the farming system ranged from 136.68 to 239.20 mg(CaCO₃)/L, which reached maximum peak value of (238.22±5.44) mg (CaCO₃)/L on the 6th day, after which it decreased gradually and then remained stable. Bio-floc had a crude protein content of 30% dry weight. The acquired sequences of 20 bands in 16S rDNA DGGE gel and six bands in 18S rDNA DGGE gel were analyzed by BLAST searches against the NCBI GenBank database. The main prokaryotic microorganisms represented by the 20 main bands in 16S rDNA DGGE gel were Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Actinobacteria, and Bacteroidetes. Alcaligenaceae throughout the process of formation of the bio-floc, and was the dominant bacteria on the 5th, 10th, and 15th days. The existence of Alcaligenaceae had some influence on the increase in water alkalinity during this period. We also found that bands 7 and12 represented Cyanobacteria, which appeared on the 0th, 5th and 10th days; they disappeared in the late culture period, which indicated that the application of bio-floc technology can control algal growth to some extent. The main Eukaryotic microorganisms represented by the six main bands in 18S rDNA DGGE gel were Loxophyllum sp., Nitzschia amphibian, Goniomonas sp., and Cryptomonadaceae. Nitzschia amphibian belongs to the diatoms, and was present from the 1^stto 15^th days of bio-floc culture. A larger number of Loxophyllum sp. existed at the later stage of the bio-floc culture. The results demonstrated that the bio-floc system achieved stable operation state after 15 days. Bio-floc could regulate the water quality and the distribution of bacteria and algae effectively; it could also maintain the balance and development of the whole aquaculture system.