The Degradation Mechanism And Characteristics Of Environmental Response Of The Atrazine-Degrading Strain DNS32

The bioremediation has been the main method in the remediation of the atrazine-contaminated soil. In Hei Longjiang Province, large usage amount of atrazine caused heavy pollution to the black soil zone, and threatened the food security in China. So it is necessary to study the the bioremediation technology aming at the emediation of the atrazine-contaminated soil in the black soil zone in Hei Longjiang Province, and find the strain which has advantages in remediation. Strain DNS32, which was isolated from black soil in this study, can utilize atrazine as the sole nitrogen source for growth. In this study, the basic degradation characteristics, the degradation pathway, the response of the DNS32strain to the oxidative stress caused by atrazine and the inorganic nitrogen were studied. The main study contents and results as follows:The objective was to study the identification, degradation characteristics and the degradation pathway of the atrazine-degrading strain DNS32, and enrich the resources of atrazine-degrading bacteria. Strain DNS32, which was isolated from black soil in this study, could utilize atrazine as the sole nitrogen source for growth, and its basic degradation characteristics were studied. The16S rRNA gene phylogenetic analysis was used to identify of the strain DNS32. The degradation pathway was studied by degrading genes amplification and the measurement of the content of the final catabolite. The results showed that strain DNS32had greater degradation capacity, it can degrade97.63%of the100mg/L atrazine in the culture medium, and could utilize certain amount of atrazine even under a relative low temperature, the atrazine degradation rate could be18.12%even under5℃. The16S rRNA gene phylogenetic analysis showed that the16S rRNA gene sequence of the strain DNS32had a99%similarity with that of Acinetobacter Iwqffii. Atrazine-degrading genes trzN, atzB and atzC were amplified by PCR, and these genes enabled strain DNS32decompose atrazine to cyanuric acid, in accordance with the degradation pathway of Arthrobacter aurescens TC1proved by the measurement of the atrazine degradation rate and the content of the final catabolite. This study enriched the resources of atrazine-degrading bacteria and provided useful informations to the study of the atrazine-degrading strains belonging to Acinetobacter.To investigate the oxidative stress response of antioxidant enzymes in atrazine-degrading bacterium exposed to atrazine played a significant role in the application of bacterium. Acinetobacter Iwoffii DNS32and Staphylococcus aureus R2cultures were treated with different concentrations of atrazine. After exposure to atrazine for0,6,12and24h, bacterial cells were harvested in order to assay SOD, CAT, GST activities and T-AOC. The results indicated that at6h T-AOC was induced, and the biggest inducement rate of SOD, CAT and GST activities were111.26%and55.47%,72.79%and61.61%,33.35%and52.76%in the two bacteria, respectively. At24h SOD and CAT in A. Iwoffii DNS32were induced, and GST and T-AOC were inhibited. But SOD, CAT, GST activities and T-AOC in Staphylococcus aureus R2were inhibited at24h. Compared with Staphylococcus aureus R2, Acinetobacter Iwoffii DNS32had relatively higher tolerance to atrazine stress and better ability to remove toxic and harmful substances. DNS32strain would be efficient when it is applied to remediation due to its good ability to tolerate atrazine in environment.Inorganic nitrogen is an important component of soil. Many studies showed that the inorganic nitrogen could restrain the degradation ability of some atrazine-degrading strains, so we study the characteristics of DNS32strain’s response to inorganic nitrogen. The degradation ability of DNS32strain in culture medium with nitrate nitrogen (KNO3) and ammonium nitrogen ((NH4)2SO4) was studied, and the influence of inorganic nitrogen on the expression of the degrading genes was studied by RT-qPCR. The results showed that the inorganic nitrogen in culture medium could promote the growth and the ability to degrade atrazine of DNS32strain, which made the DNS32strain completely degrade100mg/L atrazine in36h. The inorganic nitrogen could increase the expression of the trzN and atzBC. Compared with the control treatment, the expression of trzN gene in the treatments with inorganic nitrogen could be11.25±2.40-folds. The atrazine-degrading enzyme coded by the three degrading genes may be constitutively. The inorganic nitrogen may enhance the ability of the DNS32strain to tolerate the oxidative stress caused by atrazine, thus, the expression of the three degrading genes increase. The results showed that the DNS32strain has advantages in remediation of the contaminated black soil, because it won’t be restrained by the inorganic nitrogen in the soil.