The Selection And Identification Of Probiotic Microbes And Their Application In Turbot Culture System

This paper mainly studied on the application of three strains of probiotics in turbot culture system. The experimental targets included enrichment, isolation, selection and identification for the probiotic bacteria. By using biofilm which was build from the probiotic microbes, the changes of NOi'-N and NH4+-N in a recirculating culture system were monitored. While the security of these probiotic microbes to turbot culture had also been examined in the present study.The probiotic microbes were originally isolated from the mud in shrimp ponds, in which enrichment and selection were carried out by using selective culture medium. Eventually, 4 strains of nitrobacteria were obtained, numbered XI, X2, X3 and X4; 6 strains of nitrite bacteria were gained, numbered Yl, Y2, Y3, Y4, Y5 and Y6; 3 strains of ammonia-oxidation bacteria were acquired, numbered Al, A2, A3. Comparing to the degradation rate of NO2~-N and NH4+-N, the result indicated that X3, Yl and A3 were the best, whose degradation rate were 31.9%, 77.4% and 25.3%. The degradation rate of the rest 3 strains of nitrobacteria were 25.1%, 26.2%, 19.3%; Y2, Y3, Y4, Y5 and Y6 were 72.5%, 70.7%, 70.8%, 70.3%, 56.2%; Al, A2 were 7.37% and 12.5%, respectively.Two methods for bacterial identification were adopted, namely API-system and 16S rRNA gene screening analysis. The strain X3 was Gram-positive, short bacilliform or spherical, belonging to Rhodococcus sp.; the strain Yl was Gram-negative, spherical, belonging to Halomonas sp.; while the strain A3 was Gram-negative, short bacilliform, belonging to Nitrosomonas sp..The security of the probiotic microbes in a culture system was estimated, in which turbot larvae aging 25 days were respectively immersed into six strains ofprobiotics (X3. Y1. A3. J3. J7and J8, their final working concentration about 107CFU/mL). Compared the death of tested fish to the control group, there were no difference, indicating the strains of probiotics were safe for the cultured turbot.X3, Yl, A3, J3, J7 and J8 were cultured and then mixed to get 500L bacterial liquid in a big container. The growth of the microbes for some days allowed the volume added up to 1M3. A kind of fiber material as a carrier was then transferred to the container, allowing the microbes adhered onto it. During the experiment, regularly supplying nutrition, examining the changes of water quality such as temperature, pH, and dissolved oxygen, to assure the good conditions for the bacterial growth. After 2-3 weeks, biofilms with numerous bacteria was established.Putting the biofilm into wastewater derived from turbot culture tanks, and then the changes of NH4+-N , NCV-N and NO3N were examined. The results indicated that NH4+-N lowered from 0.300mg/L to 0.060mg/L, the degradation rate being 80%; NO2"-N and NO3"-N increased from 0.016mg/L to 0.052mg/L, 0.360mg/L to 0.390mg/L, respectively. While the COD of wastewater changed from 4.42mg/L to 2.17mg/L, the degradation rate was 50.9%.Purifying efficiency of 3 bacterial strains (Yl, A3 and X3) on wastewater from turbot culture tanks were examined on site. The experiment showed that there were some difference between site testing and laboratory testing, The degradation for NH4+-N acted by Yl and A3, they were tested as 42.3%, 44.1%, individually. While the degradation for NC>2~-N acted by X3, it was tested as 14.9%. However, the degradation by Yl, A3 and X3 in laboratory, were 77.4%, 25.3% and 31.4%, respectively.