Study On The Interfacial Action Of Arthrobacter Sp.DNS10 With Typical Minerals And Degradation Effect Of Atrazine In Adsorbed State

Atrazine is a triazine herbicide widely used in northeast China,and its residue in soil will pose a great threat to the production of sensitive crops and ecological environment.Minerals constitute the main skeleton of the soil,and atrazine will adsorb and bind with minerals after entering the soil environment.This adsorption directly affects the migration and bioavailability of atrazine,so reducing the accumulation of atrazine on the surface of minerals is a key process to reduce its residue in the soil.Microbial remediation is an efficient and green technology to reduce the residues of organic pollutants.Therefore,it is of great significance to understand the effects of soil minerals on microorganisms and the degradation of atrazine adsorbed on the surface of minerals.The microbial degradation of pollutants on mineral surface was rarely reported in previous studies,and the microbial degradation law of atrazine on mineral surface was still unclear.In this study,montmorillonite,kaolinite and goethite were selected as typical minerals,and Arthrobacter sp.DNS10,the atrazine-degrading bacteria previously screened by our laboratory,was selected as the test strain to explore the effects of these three typical minerals on the growth,biofilm formation,survival and expression of atrazine dechlorohydrolase gene（trz N）.Two types of minerals（montmorillonite and goethite）,which had obvious effects on the membrane survival and degradation potential of the strain,were selected to study the adsorption characteristics of atrazine on the surface of the above two types of minerals and the degradation rule of the adsorbed state of atrazine on the surface of minerals,so as to reveal the difference of microbial degradation rate of atrazine on the surface of different minerals and the coupling relationship between microbial and typical mineral interface processes.The findings are summarized as follows:（1）The effects of different minerals on the growth(OD₆₀₀)and biofilm formation(OD₅₉₅)of strain DNS10 were studied.The results showed that in the control group and the experimental group supplemented with montmorillonite,kaolinite and goethite,the OD₆₀₀value of strain was0.39±0.02,0.33±0.01,0.21±0.01,0.28±0.02,respectively,indicating that montmorillonite had the most obvious promotion effect on the growth of strain,followed by kaolinite,and goethite inhibited the growth of strain.The OD₅₉₅values were used to reflect the biofilm formation of the strain.The OD₅₉₅values of the control group and the experimental group supplemented with montmorillonite,kaolinite and goethite were 2.20±0.07,3.12±0.04,3.24±0.18,2.09±0.07,respectively.The biomass of the strain biofilm on the surface of the three minerals was goethite>kaolinite>montmorillonite.These results indicated that the effects of minerals on the growth and biofilm formation of strain DNS10 showed opposite trends.（2）The effects of different minerals on the expression of atrazine dechlorohydrolase gene（trz N）and cell survival in strain DNS10 were studied.The results showed that the expression level of trz N gene in the experimental groups supplemented with montmorillonite,kaolinite and goethite was 0.94 times,0.27 times and 0.20 times of that in the control group,respectively,indicating that montmorillonite had the least effect on the degradation potential of strain,followed by kaolinite,and goethite had the most obvious inhibition on the degradation potential of strain.The survival rate of strains in different mineral systems was 53.80%for montmorillonite>40.80%for kaolinite>28.20%for goethite.In addition,the fluorescence intensity of reactive oxygen species（ROS）induced by different minerals was goethite>kaolinite>montmorillonite.These results indicated that goethite induced bacterial strains to produce more ROS,resulting in decreased bacterial survival rate,at the same time,the needle-like structure of goethite can cause cell damage or even death.While montmorillonite had the least effect on bacterial survival.（3）The adsorption of atrazine on the surface of montmorillonite and goethite was studied.The adsorption kinetics results showed that the adsorption capacity of montmorillonite and goethite on atrazine reached equilibrium at 24 h,with the adsorption capacity of 3.00 mg·g^-1and2.20 mg·g^-1,respectively.The adsorption process of montmorillonite and goethite on atrazine conforms to the pseudo-second-order kinetic model（correlation coefficients are 0.998 and 0.997）,indicating that the adsorption of two minerals on atrazine is a chemical adsorption process or a chemical bonding process.The model fitting results show that the intra granular diffusion is not the only rate-limiting step for the adsorption of atrazine by montmorillonite/goethite,but the result of multiple processes.The isothermal adsorption results show that the K_Lvalue of montmorillonite on atrazine（0.04）is greater than that of goethite（0.03）,it shows that montmorillonite has stronger adsorption capacity for atrazine.The adsorption of the two minerals on atrazine is in line with Langmuir equation（correlation coefficients are 0.96 and 0.95,respectively）,indicating that the adsorption may be a single molecular layer process.（4）The degradation of atrazine adsorbed on mineral surface by strain DNS10 was studied.During the degradation process,the actual residual concentration of atrazine in montmorillonite and goethite system was always lower than the predicted value calculated by the fast equilibrium and first-order coupling dynamics model,indicating that strain DNS10 could directly degrade the adsorption of atrazine on the surface of montmorillonite and goethite.The degradation rates of strain DNS10 on the surface of montmorillonite and goethite were 94.00%and 78.00%,respectively.The degradation rates of strain DNS10 on the surface of montmorillonite were more thorough.The differences in the above degradation rates were analyzed from the perspectives of biofilm biomass and strain survival rate.The results showed that:The OD₅₉₅values of montmorillonite/goethite and atrazine composite system were 1.72±0.13 and 3.10±0.17,respectively.The biofilm biomass of strain DNS10 on the surface of the goethite and atrazine complex was higher than that of montmorillonite and atrazine complex.However,the survival rate of the strain on the surface of goethite and atrazine complex（37.20%）was lower than that of montmorillonite and atrazine complex（67.80%）.These results indicated that strain DNS10 formed less biofilm after adsorption of atrazine on the surface of montmorillonite,but the survival rate of strain DNS10 was higher,which was conducive to the biodegradation of atrazine on the surface of montmorillonite.After the adsorption of atrazine on the surface of goethite,the biofilm biomass of the strain was higher,but the survival rate of the bacteria was lower,which was not conducive to the biodegradation of atrazine adsorbed on the surface of goethite.