Isolation,Characterization And Metabolic Mechanism Of Atrazine Degrading Consortium And Its Remediation Effect

Atrazine was developed by Switzerland Ciba-Geigy Company in the 1950s and has been used extensively all over the world due to its cheapness and good herbicidal ability. Atrazine is mainly used to prevent annual grass and broadleaf weeds in corn, sorghum and sugarcane fields. However, the frequent use of atrazine in large quantities to farmland, can contaminate the farmland including the water body around the land, destroy the ecological environment and threaten public health eventually. What is more its residue in soil could cause phytotoxicity to succession sensitive crops to some extent. In this study, a consortium capable of degrading atrazine was isolated from soils and used to examine degradation characteristics and proposed metabolic mechanism. The results were summarized as follows:A consortium capable of utilizing atrazine as sole source of carbon and nitrogen was isolated from atrazine contaminated soils. Based on the phylogenetic analysis of 16S rDNA gene sequence,their morphological and physiological characteristics, the consortium was composed 10 strains including Pimelobacter sp.Al, Arthrobacter sp. A2, Arthrobacter sp. A3, Ancylobacter sp. A4, Gordonia sp. A5, Xanthobacter sp. A6, Bacillus sp. A7, Pseudoxanthobacter sp. A8, Mesorhizobium sp. A9, Azospirillum sp. A10. Isolate strain A3, A4, A6 and A7 showed atrazine degrading ability. The consortium haboured triazine hydrolases gene trzN, hydroxyatrazine ethylamino amidohydrolase gene atzB, N-isopropylammelide isopropyl amine amidohydrolase gene atzC, atrazine chlorohydrolase gene atzA and cyanuric acid amidohydrolase gene rrzD. A3, A4, A5, A6, A7 haboured triazine hydrolases gene trzN; A3, A4, A6, A7 haboured hydroxyatrazine ethylamino amidohydrolase gene atzB; A3 haboured N-isopropylammelide isopropyl amine amidohydrolase gene atzC.The degradation characteristics of atrazine by the consortium mainly depends on substrate concentration, temperature and pH. Under the condition of pH7.0,30℃, the degradation rate of 1mg/L atrazine was 70.0% after 48h incubation, the residue of 10mg/L atrazine was below the detection limit(0.01mg/L)after 48h incubation, the degradation rate of 100mg/L atrazine was 65.2% after 48h incubation. Under the condition of pH7.0, 10mg/L,20℃ atrazine degradation rate was 58.6% after 72h incubation,30℃ atrazine residue was below the detection limit after 72h incubation, however, when temperature was 40℃, no obvious degradation happened compared to the control. Under the condition of 30℃, lOmg/L, pH7.0 atrazine residue was below the detection limit after 48h incubation; pH9.0 atrazine degradation rate was 85.8% after 48h incubation; while, pH5.0 showed no apparent degradation effect. Taking all factors into consideration, the atrazine degradation rates at different substrate concentration, pH and temperature varied with the order of 100mg/L> 10 mg/L> lmg/L,30℃> 20℃> 40℃, pH7.0> pH9.0> pH5.0, respectively.The analysis result of UPLC-Q-TOF-MS and HPLC-MS/MS indicated that the metabolites in atrazine degradation consisted of hydroxyatrazine, N-isopropylammelide, cyanuric acid and allophanate. The degradation of atrazine by the consortium was a mineralization process, which involving dechlorination, hydrolization, dealkylation, deamination and the ring cleavage of the heterocycle.The result of bioassay indicated that the consortium has efficient capacity of remediating the pollution caused by atrazine. In water culture experiment, comparing with the rice in the same atrazine concentration without inoculation treatment, the inhibition ratios of plant height, fresh weight and dry weight of rice was decreased by 39.6%,40.0% and 40.9% respectively in treatment with atrazine and inoculation, and the latter was basically identical with the control (without atrazine and inoculation). In soil experiment, comparing with the rice in atrazine treatment without inoculation the inhibition ratios of plant height, fresh weight and dry weight of rice was decreased by 30.3%,33.3% and 14.2% respectively in treatment with atrazine and inoculation, which was basically identical with the control(without atrazine and inoculation). The results showed that the consortium could reduce the inhibition on the rice growth caused by atrazine.