Isolation And Identification Of Bacteria From Bio-floc And Their Characteristics Analysis

This experiment isolated bacteria from the biological floc, and studied theirproperties, investigated the safety of the bacteria for Litopenaeus vannamei,screened bacteria were used to culture bio-floc. The main results were as follows:1Isolation and identification of nitrosobacteria from bio-floc and theircharacteristics analysisTwo strains with high ammonia transforming rate were isolated by enrichmentculture and separation purification from bio-floc of shrimp culture ponds. Sequence of16S rDNA suggested that both the two strains belong to the genus of Halomonas sp.,the strain2011072708was identified as H. alimentaria with similarity of99%, andthe strain2011072709was identified as H. shengliensis with similarity of100%.Ammonia transforming rate of the two strains were compared in different temperature,salinity, pH, and C/N ratio, ammonia transforming rate of the strain2011072708reached highest level at the condition at37°C, salinity3040, pH8, and C/N ratio28;and the strain2011072709reached highest at the condition at27°C42°C, salinity4050, pH6, and C/N ratio21. The study showed that the two nitrosobacteria strainsisolated from bio-floc both had high ammonia transforming rate. H. shenliensis(2011072709) has better adaptability to temperature, salinity, pH, and C/N ratiothan H. alimentaria(2011072708) and may be more suitable for the application inbio-floc technology.2Isolation, identification and its characteristics analysis of a nitrobacteriumfrom bio-flocA strain with high nitrite moval ability were isolated from bio-floc of shrimpculture ponds.Sequence of16S rDNA suggested that the strain belong to the genus ofHalomonas sp., the strain was identified as H. alimentaria with similarity of99%.The effects of different C/N ratio, pH, salinity, temperature on nitrite moval ability ofstrain201205250102were studied, nitrite moval ability of the strain201205250102 reached highest level at the condition at C/N radio15, salinity30-40, pH8.0-10.0,temperature37℃,the highest of nitrite moval rate was91.69%. The study isolated anitrite removal strain from the bio-floc of shrimp culture ponds, which furtherenriched the germplasm resources of nitrobacterium and provide theoretical basis onpractical use of stain201205250102in bio-floc culture Technology.3Screening and identification of a potential probiotic from bio-floc and theircharacteristics analysisThree strains of beneficial bacteria were isolated by antagonistic test frombio-floc of shrimp culture ponds. Sequence of16S rDNA suggested that the strain2011072709was identified as H. shengliensis with similarity of100%. The strain2012052503was identified as Bacillusmegaterium with similarity of99%.the strain2011072701was identified as Halomonas sp.with similarity of99%. Hemolysis testconfirmed that the three strains could not produce hemolysin, which did not have thepotential pathogenicity; drug sensitivity test showed that strain2011072701and2011072709was resistant against10kinds of antibiotics; while the strain2012052503was resistant against penicillin, and was sensitive to the rest19kinds of antibiotics;animal security tests showed that when concentration of strain was below107CFU/Ml,they showed no apparent toxic effects on the experimental shrimps. Therefore, thethree strains could be applied in production.4Effect of adding bacteria and sucrose on the formation amount of bio-flocIn order to study the effect of adding bacteria on the formation amount ofbiol-floc, three different strains of bacteria were added into Litopenaeus vannameifarming waters, and sucrose was added as organic carbon source. After being culturedfor6days, the amount of bio-floc could keep a stable population at concentration of5g/L in sugar and bacteria addition group, which incresed significantly compared withthe control group(P<0.05). Therefore, the three strains could improve the formationamount of bio-floc significantly under the sucrose addition conditions, which could beapplied in bio-floc culture, and this experment could provide a guarantee for furtherstudy of the impact on the water quality of bio-floc.