| High density aquaculture mode in the modern times,the large bait and excrement in the breeding process,animals and plants and other organic compounds containing nitrogen pollution is serious,so the screening experiments using ammonia and nitrite nitrogen degradation ability as the main screening indexes of objective strain.In this experiment,we had selected a strain of heterotrophic nitrification and aerobic denitrification bacteria,and had carried on the nitrogen removal performance test,strain identification,fermentation medium and culture condition optimization,and analyzed the safety of the use of strains to the culture of Litopenaeus vannamei and the nitrogen removal effect in L.vannamei culture ponds.The main results were as follows:Part one: isolatation and identification of heterotrophic nitrification-aerobic denitrification bacteriaIn order to obtain stains with high heterotrophic nitrification and aerobic denitrification efficiency,10 strains were isloated from the laboratory saving.The strain named 7-3 with high ability of heterotrophic nitrification and aerobic denitrification were selected from the 10 strains.The 48 h ammonia nitrogen degradtion of strain 7-3 was 99.00%,total nitrogen degradtion was 68.13%,nitrate nitrogen was 47.37% and nitrite nitrogen degradtion was 100%.In the light of their morphological and physiological features as well as the 16 S rRNA sequences,strain 7-3 were identified as Arthrobacter mysorens.The growth characteristics of the strain 7-3 showed that the 0~6 h was in a slow phase,and then entered the logarithmic growth phase after 6 h,the maximum growth rate reached the maximum after 33 h,and the n entered the stable stage,and then the bacteria entered the decline stage after 48 hPart two: the optimization of the liquid fermentation medium and conditions of Arthrobacter sp.7-3.The liquid fermentation medium and conditions of Arthrobacter sp.7-3 were optimized by single factor experiments and orthogonal experiments.The results indicated that the composition of corn meal 1%,yeast 1%,K2HPO4 0.2% and KH2PO4 0.2% were selected to be the medium formula,and the fermentation conditions were the inoculum 7%,the temperature 25 ?,rotational speed 220 r/min,initial pH at 8.0 and liquid volume 100 mL for 48 h,and.Under the optimized fermentation conditions the production of living cell was up to 4.04×1010 CFU/mL.Part three: experimental study on the safety of the strain to L.vannamei.Three bacteria strains were set to 104 CFU/m L,106 CFU/mL,108 CFU/mL concentration gradient and were added to the 5 L shrimp culture container.The results showed that strain F1508 was 108 CFU/mL concentration in water,the cumulative mortality of shrimp no significant difference with the control group;strain 7-3 and 683 was 106 CFU/mL concentration in water,the shrimp cumulative mortality rate had no significant difference with control group.When the strain F1508 was used below the concentration of 108 CFU/mL and the strain 7-3 and strain 683 were below the concentration of 106 CFU/m L,it was safe to use in shrimp culture.Part four: removal of ammonia nitrogen and nitrite nitrogen from the pond of culturing L.vannameiThe compound bacteria was applied to the aquaculture ponds of L.vannamei and the test period was 15 d,and the concentrations of ammonia nitrogen and nitrite nitrogen were detected by sampling every day.The experimental results show that the degradation effect of compound bacteria on both ammonia and nitrogen in aquaculture water and nitrite-N the maximum ammonia nitrogen removal rate reached 80.31%,nitrite nitrogen removal rate reached 85.58%,effect on water pH were not significant,the fluctuation of pH value in the range of 8.1~8.3. |
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