Study On T He Aerobic Denitrification Characteristics Of Pseudomonas Fluorescens YSD-1 And The Enhanced Treatment Of Simulated Aquaculture Circulating Water

China is a large aquaculture country,and the technology of recycling aquaculture system(RAS)has been widely used and developed in China.However,the high-density culture,the residual feed and the lack of denitrification lead to the accumulation of nitrate in Ras.It is difficult to realize the traditional denitrification process and the requirement of total nitrogen removal under high dissolved oxygen,and with the accumulation of nitrate,there will be problems such as the destruction of physiological mechanism of aquaculture products,the inhibition of growth rate,the reduction of survival rate,and even death.In this paper,a strain YSD-1 with efficient aerobic denitrification function was screened from the nitrification activated sludge,and a series of studies were conducted on it.The results are as follows:(1)YSD-1 was identified as Pseudomonas fluorescens by morphological observation and molecular biology,and named as Pseudomonas fluorescens YSD-1.The growth curve was in accordance with the growth characteristics of general type(S type)of bacteria.(2)When the concentration of NO₃^--N was 100 mg/L and 300 mg/L,the removal rate of NO₃^--N was over 80%,and there was no NO₂^--N in the denitrification process;when the concentration of NO₃^--N was 500 mg/L,it was only 23.1%.Under the condition of high concentration of NO₃^--N,the denitrification of strain P.fluorescens YSD-1 was obviously inhibited.The results of quantitative q PCR showed that the expression levels of nap A,nir S and nir K genes c hanged with time.It was confirmed that there was an aerobic denitrification pathway of NO₃^--N?NO₂^--N?NO in strain P.fluorescens YSD-1.The coexistence of nir S and nir K indicated that there was no nitrite accumulation in denitrification.(3)The optimal medium was determined to be 2.1g of potassium nitrate,10g of sodium acetate,1.5g of disodium hydrogen phosp hate,1.5g of disodium hydrogen phosphate,0.1g of magnesium sulfate heptahydrate and 1 m L of trace elements(/L);the optimal denitrification conditions were 180r/min,33?temperature,7.5 initial p H and 89.5%of NO₃^--N.(4)Two sets of reactors were designed to treat the simulated breeding circulating water,and the experimental group added P.fluorescens YSD-1 for biological enhancement treatment.The average removal rate of NO₃^--N increased by 4.40%.It shortens the time of stable effluent of the reactor.P.fluorescens YSD-1 was successfully colonized in sludge.The relative abundance of Pseudomonas in the experimental group was 6.61%,3.17%,3.70%,and the control group was 0.17%,0.11%,0.10%.There was no significant difference in the sludge level between the experimental group and the control group.The addition of exogenous microorganism P.fluorescens YSD-1 did not greatly disturb the microbial community structure of the sludge,and did not destroy the original ecosystem balance.The relative abundance of P.fluorescens YSD-1 in sludge was 0.17%,0.11%,0.10%in the control group,and 6.61%,3.17%,3.70%in t he experimental group.There was no significant difference between the experimental group and the control group at the genus level.The addition of exogenous microorganism P.fluorescens YSD-1 did not disturb the microbial community structure of sludge greatly and did not destroy the original ecosystem balance.Through the analysis of 16Sr DNA function prediction,it can be seen that P.fluorescens YSD-1 enhanced the denitrification metabolic pathway of the community.