Isolation,Identification And Degradation Characteristics Of Deltamethrin-Degrading Bacterial Strain

Pyrethroids pesticides are a class of pesticides by artificially synthetic natural pyrethroids,which effectively overcomes the adverse effects of traditional organophosphorus,organochlorine and carbamate pesticides on the environment and human health.Due to the characteristic of high performance,broad-spectrum,safety and low-poison to people and livestock,pyrethroids have been widely used in aquaculture and agricultural pest control.The commonly used pyrethroid pesticides include deltamethrin,cypermethrin,fenvalerate and fenpropathrin.Deltamethrinin?DM?is one of the most effective species of pyrethroid,which has been widely used in the world,and is one of the fastest-growing pesticides in China.In recent years,deltamethrinin has a good effect on the control of common freshwater fish parasitic protozoa,anchors,fish lice and other crustaceans parasite.With the increase usage of deltamethrin,the residue of deltamethrin in fishery waters is corresponding growing,which does great harm to the water environment.Since the second generation pyrethroid insecticides have the characteristics of light tolerance and heat resistance,they remain longer in the environment and are highly toxic to aquatic organisms,which are likely to lead to breeding accidents in aquaculture.Therefore,it is necessary to eliminate or reduce the residue of deltamethrin in water environment.Microbial remediation has the advantages of high efficiency,non-toxicity,no secondary pollution,easy operation and low cost,which provides hope for reducing pesticide residues in agricultural products and agricultural production environment.At present,it has become an important method to remove pesticide residue pollution.Whether the biodegradable bacteria can be applied to the production practice,keep stable quantity and high degradation activity in the external environment is an urgent problem to be solved in bioremediation technology.At present,there are many researches about bioremediation of pesticide residues in vegetables and soils by biodegradable bacteria.However,the screening of pyrethroid degrading bacteria and the mechanism of degradation of pyrethroid pesticides in freshwater environment and sediments have not been systematically studied.Soil samples were collected from the plowland soil exposed to repeated pesticides contamination,which was cultured at inorganic salt medium prepared by adding deltamethrin as the sole carbon source.The degradation ability of degrading bacteria were determined by gas chromatography to screen and identify a relevant high-efficiency degrading bacteria strains named SW.The best degradation conditions of strain were studied by changing the external conditions such as temperature,pH,inoculation,initial concentration of deltamethrin and different pesticide substrates,and the effect of bioremediation of deltamethrin in cultured freshwater was explored.This study can provide theoretical and technical support for the establishment of an effective microbial remediation technology for deltamethrin residues in cultured freshwater environment,protecting freshwater environment and controlling pesticide residue pollution in aquaculture environment.In our research,the deltamethrin degrading bacteria was isolated from Sphingobacterium sp.for the first time,which provided a new strain resource for the biodegradation of pyrethroids and enriched the diversity of pyrethroid pesticide degrading bacteria.The main contents are as follows:1.Collecting the plowland soil exposed to repeated pesticides contamination.Soil samples were cultured at inorganic salt medium prepared by adding deltamethrin as the sole carbon source.The degrading bacteria were acclimated gradually by cultured in different concentration of deltamethrin.The single colony was isolated from the plate coated with the last acclimated medium,and the different strains which grew well on the medium and subcultured stably were numbered.The degradation ability of degrading bacteria were determined by gas chromatography.A deltamethrin-degrading strain was isolated and named as SW.Based on the morphology,physio-biochemical characteristics,and 16S rRNA sequence analysis,strain SW was temporarily identified as Sphingobacterium multivorum.Strain SW not only could utilize deltamethrin as the sole carbon source for growth in mineral salt medium,but also could highly tolerate and efficiently degrade deltamethrin.When bacterial strain SW was incubated in mineral salt medium contained 1.0 mg·L^-11 deltamethyrin at pH 7.0 after 5 d shaking at 180r·min^-11 under 30?,the degradation rate of deltamethyrin reached 76.4%.2.Several experiments were performed to investigate the factors affecting the degrading characteristics.The main factors affecting the degradation of pesticides by microorganisms include the properties of microorganisms,the structure of pesticides and the external environment.The best degradation conditions of strain were studied by changing the external conditions such as temperature,pH,inoculation,initial concentration of deltamethyrin and different substrates,so as to provide the basis for further research and application.The optimal conditions for biodegradation were obtained as follows:30?,pH 6.0 and inoculum biomass 4%.Strain SW could efficiently degrade deltamethrin(0.1,0.5 and 1.0 mg·L^-1)with degradation reaction followed first-order kinetics and half lives(T_1/2)were 4.5,2.3 and 2.0 d,respectively.Strain SW could degrade 0.5 mg·L^-1cypermethrin,fenvalerate and fenpropathrin to some extent with gradation rates of 33%,30%and 26%within 5 days of incubation.3.Strain SW could degrade 0.5,5.0 and 50?g·L^-1deltamethrin in freshwater with degradation rates of 21.6%,26.4%and 53.8%in 5 days through bioremediation.SW?Sphingobacterium multivorum?is isolated and has some remediation effect on freshwater contaminated by deltamethyrin,which can be used in pyrethroid pesticide pollution bioremediation as a biodegradable bacterium resource.4.The fermentation conditions and optimum mediums of the degradation bacterium were optimized by single factor analysis.When the pH was 7,the carbon source was 2.0%amylogen,the nitrogen source was 1.0%yeast extract powder,inorganic salt was 0.5%potassium hydrogen phosphate,the temperature was 35?,rotating speed 160 r·min^-1,and the inoculation amount was 6%,the strain SW grew fastest.