| In this study, five strains of bacillus bacteria were isolated at last. In the study,the strains were selected with a series method of laboratory experiment which wasincluding of enriching and culturing the bacterial samples taken from shrimp (Penaeusvannamei Boone) outdoor ponds. Then we studied the optimizing and compounding ofsome high effective strains, specific degrading characteristics of one special strain, allof which were screened from the bacteria above. The main results were detailed asfollows:1. Enrichment, domestication, isolation and selection of probiotic bacillus bacteriafrom shrimp (Penaeus vannamei) outdoor pondsIn this study, by series of enrichment and domestication, the normaltemperature (28±1)℃bacillus bacteria was isolated and screened from shrimpculturing ponds. And five normal temperature strains was selected eventually, namedE1, E6, E13, E15and E21respectively. These strains can removal some componentsof shrimp feed highly, such as ammonia nitrogen and nitrite. The study showed thatdegradation effect of different strains varied from ammonia nitrogen and nitrite ofshrimp feed. E1, E6and E15were the best degrading strains in terms of ammonianitrogen with the degradation rate of44.20%~48.20%in the fifth day. As to thedegrading of nitrite, E1, E6, E15and E21all had a high degradation rate and thedegradation rate of nitrite was up to70.00%in the fifth day, of which the best strainswere E6and E15, the nitrite degradation rate of E15was up to99.72%in five days,while the E6removed the nitrite in shrimp feed completely (degradation rate of100%) in five days. At last four strains were selected for further studied according to thecombined effects of ammonia nitrogen and nitrite degradation. Based on the bacteriaform, physiological and biochemical detection and the analysis of16SrDNA similarysequences, the four strains were all identified as Bacillus spp., E1as Bacillusmegaterium, E6as Bacillus pumilus, E15as Bacillus licheniformis.2．Study of one high effective Bacillus strain on degrading characteristicsThis study was investigated about one high effective feed-degrading bacteriastrain which was named E6, by studying its degrading capability of NH3-N andNO2-N in shrimp feed. Studies had shown that the strain E6had good growth anddegradation characteristics. Result about the growth characteristics showed that thestrain grew rapidly in (6-22) hours and to achieve the maximum in24hours,6-14hours was growth logarithmic phase of E6. This study also included the dynamicprocess on degradation and the different effects of E6majorization on the degradationof shrimp feed. Further study was done for the best E6about its specific degradingcharacteristics in order to learn more mechanism of E6, the aspects mainly includingits optimal temperature, optimal salinity and optimal pH for feed degrading. Theresults showed that the strain of E6significantly had the dynamic process ofdegradation, which the ammonia nitrogen in enriched medium reached the lowest inthe first two days after inoculation E6, the degradation rate of up to57.27%. Besides,the nitrite in the feed had been reduced continuously in5days and the content ofnitrite was as low as0.25mg/L in the forth day which had the degradation rate ofnitrite up to98.02%, in5days, the nitrite was completely removed(degradation rate of100%). Further degrading studies of strain E6showed that the appropriate range oftemperature, salinity and pH value for growth was (24～36)℃,(1-8)%and7.0～8.0respectively, while the optimal temperature, salinity and pH value conditions for feeddegrading was (24～32)℃,(3-6)%and7.5～8.0respectively.3. Preliminary study of degrading on optimizing and compounding of probioticBacillus strains This study was about the effect of dynamic degradation of single strains and theoptimizing and compounding of probiotic Bacillus strains which had high effectivedegradation characteristics, according to the effects of bacterial combinations on thedegradation of ammonia nitrogen and nitrite in shrimp feed, then the best combinationwas selected. The results showed that the four strains (E1, E6, E15and E21) all hadhigh effective on degradation of NH4-N in two days, with the degradation was50.90%,57.27%,46.77%and50.54%, respectively. The degradation of NH4-N was ashigh as40%in five days besides E1. The four strains all had a high degradation rateof nitrite in shrimp feed, which strains E15and E21had the degradation up to97.78%and93.07%respectively in three days, the nitrite removal rate of strain E6was up to100%, completely removing the nitrite in shrimp feed. The result of optimizing andcompounding of probiotic Bacillus strains showed that none of combinations ofstrains was better than strain E6which was set as control because of effectivedegrading characteristics. But on degrading of nitrite, E1-E6-E15-E21was the bestbacterial combination which completely removed the nitrite in shrimp feed in twodays with the high degradation of100%and maintaining the high degradation rateuntil the end of the experiment. |
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