Study On Denitrification Performance And Key Enzyme Functional Genes Of An Aerobic Denitrifier,Pseudomonas Stutzeri XL-2

China’s long-term use of extensive economic development model brought great harm to the environment.Nitrogen pollution in the water environment is particularly serious.The traditional biological denitrification theory holds that the nitrification process is carried out under aerobic conditions.The denitrification process can only be carried out under anaerobic or anoxic conditions,and there are many drawbacks.The discovery of aerobic denitrification allows nitrification and denitrification to be performed simultaneously in a reactor with aerobic conditions,which is more efficient and efficient than conventional biological denitrification processes.In this paper,a nitrifying bacteria with aerobic denitrification was used as the research object to study its physiological and biochemical characteristics and identify its species.The effects of different environmental factors and different nitrogen concentration on the aerobic denitrification were investigated.The key enzymes of denitrification of strain XL-2 was studied by molecular biology and bioinformatics.The main findings are as follows:A strain of XL-2 with aerobic denitrification was screened from the activated sludge of the traditional denitrification process.The strain XL-2 was selected by the method of plate scribing and liquid selective culture.The strain is straight or slightly curved bacillus,seedless,does not form spores,the bacteria size is 0.45×（1.2-2.3）μm.Mature colonies were light yellow-green,irregular edges,the surface has wrinkles,moist,translucent.The strain XL-2 belongs to the genus Pseudomonas stutzeri（Pseudomonas stutzeri）by cell morphology and 16 S rDNA sequence identification.The results showed that when NO_3--N was 100 mg/L,the removal rate of NO_3--N reached 98.8%,the removal rate of TN reached 87.6%,and the contents of NO₂--N and NH₄⁺-N were not significant accumulation.At 36 h,the gaseous products of the strain XL-2 denitrification were tested,the N2O-N content was 0.501 mg and the N2 content was 2.519 mg.The results showed that the main gaseous product of the denitrification process was N2 and the conversion of NO_3--N to N2 was carried out by measuring the gaseous product of the denitrification process of strain XL-2 and combining with the nitrogen balance in the calculated nitrate medium.The aerobic denitrification denitrification performance of strain XL-2 was further verified.Further experiments showed that the strain had a good effect on 300 mg/L NO_3--N.When the concentration of NO_3--N was increased to 500 mg/L,the growth and denitrification of strain XL-2 were seriously inhibited.The effect of different environmental factors on the aerobic denitrification of the strain showed that the C/N range was 8¹5,the temperature range was 30³5 ℃,the rotational speed of the shaker was 120¹50 rpm,the strain XL-2 grew well and can achieve better denitrification effect.The removal rates of NO_3--N and TN were higher,and the contents of NO₂--N and NH₄⁺-N were not accumulated.The effects of Mg²⁺,Mn²⁺,BO₃^3-,Zn²⁺,Fe²⁺,Ca²⁺ on the growth and denitrification of strain XL-2 were studied.Mg²⁺ has the greatest contribution to the growth and denitrification of the strain,and the effect was the most obvious,followed by Fe²⁺.Ca²⁺,BO₃^3-,Zn²⁺,Mn²⁺ do not have much effect on the growth and denitrification of strain XL-2.The results showed that there were four key enzymes（Nar,Nir,Nor,Nos）in aerobic denitrification in strain XL-2,and Nar was speculated that Nitrite reductase,Nir should be cytochrome cd1 type nitrite reductase,and four kinds of enzyme protein fragments were analyzed by hydrophobic and transmembrane analysis,and the basic physical and chemical properties of four key enzymes were obtained.