Isolation Of Fomesafen-degrading Strain And Its Application On Potted Maize

Fomesafen is a herbicide widely used in peanut and soybean fields,and it has a long effective period of pesticide residue to damage sensitive next crop.In recent years,due to the increasing use of fomesafen,the residual harm is becoming more and more serious,and it is inevitable to explore a safe and effective way to solve the pollution caused by the application of fomesafen.At present,one of the main solutions to pesticide residues is to rely on microbial degradation technique,many scholars have isolated fomesafen-degrading bacteria,and proved the feasibility of microbial degradation of fomesafen.The aim of this paper is to obtain new microbial resources which are suitable for the remediation of fomesafen-contaminated soil.The fomesafen-degrading strain was isolated from the soil samples by enrichment culture and pour separation.The bioassay method for the determination of fomesafen in soil by using the above-ground fresh weight of 10-day-old maize seedlings: Y=-7.096x+3.281,R2=0.882,p=0.002?0.01.The degradability of the FCX2 strain and the FCX7 strain was tested by bioassay and high-performance liquid chromatography(HPLC),and the degradation rate of fomesafen was 44.86% and 50.79% when the initial concentration of fomesafen was 500 mg·L-1,30 ?,150 r·min-1,5 d and inorganic salt medium.The strain FCX2 and the strain FCX7 were Alcaligenes sp.and Bacillus sp.,respectively,according to the physiological and biochemical indexes and 16 S r DNA sequencing.The growth characteristics of FCX2 strain showed that the optimum temperature was 30 ?,the optimum p H was 8,the optimum carbon source was glucose and the optimum nitrogen source was peptone.The optimum medium for the growth of FCX2 strain was glucose 22.16 g·L-1,peptone 26.14 g·L-1,K2HPO4 1.76 g·L-1,KH2PO4 0.59 g·L-1,and the concentration of micronutrient was adjusted to 1.78 times of the original concentration.The maximum OD600 of FCX2 strain could reach 1.52 after 40 h culture under these conditions,similar to the optimized prediction.The growth characteristics of FCX2 strain showed that the optimum temperature was 30 ?,the optimum p H was 6,the optimum carbon source was glucose and the optimum nitrogen source was peptone.The optimum medium for the growth of FCX7 strain was market sugar 22.75 g·L-1,yeast extract 27.95 g·L-1,K2HPO4 1.09 g·L-1,KH2PO4 0.36 g·L-1,and the concentration of micronutrient was adjusted to 2.02 times of the original concentration.The maximum OD600 of FCX7 strain could reach 2.64 after 52 h culture under ii these conditions,similar to the optimized prediction.In order to ascertain the application potential of FCX2 and FCX7 strains,the effect of fermentation on seed germination was studied.The results showed that FCX2 strain or FCX7 strain could significantly promote the germination of maize seeds.Because FCX2 strain produces an extremely high p H during the fermentation process,only FCX7 strain was tested for the content of MDA and the activity of anti-stress enzyme.The results showed that the activities of SOD(Superoxide dismutase),POD(Peroxidase)and CAT(Catalase)of FCX7 were 4.53%,10.74% and 14.09% higher than those of the same dilution medium,the content of MDA decreased by 23.60%,which indicated that FCX7 could promote the germination of maize seeds.When the initial concentration of fomesafen was 0.30 mg·kg-1 in the soil and the concentration of FCX7 strain was 1×1010 cfu·kg-1 for 21 d,the degradation rate was 62.33% in HPLC detection and 44.82% in bioassay,and the fresh weight of the above-ground part of the planted maize was 39.89% higher than that of the untreated.Compared to the above-ground part of the control,the content of MDA decreased by 45.63%,and activities of CAT,POD and SOD increased by 47.64%,107.35% and 51.12% respectively.Compared to the under-ground part of the control,the MDA content decreased by 10.21%,and activities of SOD,CAT and POD increased by 41.73%,34.97% and 25.91% respectively.Activities of urease,protease,CAT,POD and POD were 5.83%,16.21%,8.1% and 10.16% higher than the control of pot soil.Comparison FCX7 treatment soil to non-FCX7 treatment soil,activities of urease,protease,CAT and POD increased by 10.15%,6.88%,8.31% and 8.82% respectively.The content of MDA decreased by 10.21%,and activities of SOD,CAT and POD increased by 7.33%,18.58% and 13.92% respectively in the above-ground part of the corn seedling.The content of MDA decreased by 15.54,and activities of SOD,CAT and POD increased by 6.77%,5.15% and 14.11% respectively in the under-ground part of the corn seedling.The result showed that FCX7 strain could improve the activity of soil enzyme and maize seedling.The degradation ability of Alcaligenes sp.FCX2 strain and Bacillus sp.FCX7 to fomesafen was confirmed by the experiment,the growth characteristics of the strain were elucidated,the medium were optimized,the degradation characteristics of FCX7 strain were further confirmed by pot culture,improving effect on seed germination and seedling growth of maize.The study provide theoretical basis,technical support and corresponding microbial resources for the research and application of fomesafen-contaminated soil.