Screening Of Soil-derived Bacteria For The Chiral Fungicide Mandipropamid And Study Of Its Degradation Characteristic

Mandipropamid,first marketed in 2003,is a carboxylic amide(CAA)fungicide developed by Swiss Syngenta and the first commercial mandelic acid amides fungicide.In 2005,the Fungicide Resistance Action Committee(FRAC)officially declared carboxylic acid amide(CAA)fungicides as group number 40 on the FRAC code list.Our previous study has shown that the half-life of mandipropamid in soil is long,which has potential environmental safety risk.Therefore,a technology to accelerate the degradation of mandipropamid residues in soil is urgently needed.Bacteria-induced biodegradation technology has become an effective way and method to remove pesticides residues in contaminated soil.This paper intends to establish an effective biodegradation method for the removal of mandipropamid residues.For the first time,dominant degrading bacteria obtained from soil contaminanted by mandipropamid were isolated and identified,and the degradation behavior of dominant degrading bacteria on mandipropamid was studies in vitro and in vivo.Meanwhile,the stereoselectivity of mandipropamid stereoisomers during biodegradation was investigated,which provided data support for soil remediation of mandipropamid pollution,its proper use and environmental safety evaluation.In this paper,seven mandipropamid-degrading bacterial strains were isolated and enriched from contaminated soil samples.Among them,three bacterial strains with high degradation efficiency(> 63%)were screened and identified as Pseudomonas sp.(M01),Mycolicibacterium parafortuitum(MW05),and Stenotrophomonas maltophilia(MW09)by morphological and 16 S r RNA gene sequencing analyses.The biodegradation characteristics of three strains was investigated,revealing that the best nutrient source was mandipropamid and the suitable inoculation amount was 5%.Other influence factors,including p H,temperature,and initial concentration of mandipropamid,significantly impacted the biodegradation efficiency.Box-Behnken model experiment and an analysis of variance were further used to determine the optimal biodegradation conditions for mandipropamid.The data showed that the best biodegradation conditions for three strains were different and the degradation efficiency was more than 96%.Mycelial,intracellular,and extracellular enzymes also affected the biodegradation of mandipropamid enantiomers by M01,MW05 and MW09.In soil remediation trials,three bacterial strains effectively and stereoselectively degraded mandipropamid in contaminanted soil samples(R-enantiomer degraded faster)and influenced the activity of urease and β-glucosidase in the soil.The above results can recommend several potential bacterial strains for mandipropamid biodegradation and provide information on biological detoxification of mandipropamid in soil environments.