Isolation Identification And Degradation Characters Of Dimethoate-Degrading Strain L3

Dimethoate is an organophosphate pesticide which has been used in large quantities throughout the world.It is used on major field crops,orchards,vegetables,and ornamentals. However,dimethoate is toxic for living organisms and environment,and it may be released to the aquatic environment via soil percolation,air drift or surface run-off due to its highly soluble in water.It is acknowledged that microorganisms play a significant role in metabolizing various pesticides both in soil and in water.So it has been an important research item for us to exploit and utilize microbial resource to remove environment pollution.This research was to isolate the bacteria that can use dimethoate as sole carbon source,study the degradation of dimethoate in liquid culture and soil,and provide the theory base for the bioremediation of environment pollution with dimethoate.One dimethoate-degrading bacterium L3,was isolated from the sludge collected from the bottom of wastewater treatment pool of a pesticide factory,was identified preliminarily as Paracoccus sp.based on its morphological characters,physiological and biochemical analyses and 16S rDNA series same source analysis.L3 can use dimethoate as sole carbon source.Biological properties of strain L3 were studied.The optimal temperature and initial pH for growth of L3 were 37℃and 7.0,respectively.Also L3 could sustain on large scale NaCl concentration（0%-6%）,and resistant tO streptomycin.The strain could grow well when using glucose or fructose as sole carbon sources,and peptone,beef cream or yeast extract as sole nitrogen sources.No plasmid was picked up from strain indicate that dimethoate-degrading gene may located in chromosome.Studies indicate that the strain could use dimethoate as the sole carbon,and degrade 100mg/L dimethoate to an undetectable level within 6h.The optimal concentration of dimethoate for growth of L3 is 300mg/L,while the concentration of dimethoate higher than 1000mg/L became toxic to the normal growth.The optimal pH and temperature for the degradation is 7.0 and 35℃,respectively.Degradation tests have revealed that L3 has degradability of dichlorovos,parathion and phoxim,and cannot degrade omethoate. Therefore,we may primarily conclude that the degradation may involved in P=S bond.Bioremediation of L3 in contaminated soil showed that the degradation of dimethoate in the soils needs soil humidity;a little high humidity benefits the biodegradation of dimethoate.The addition of L3 is able to degrade dimethoate over a temperature range of 15～40℃and pH range（4.0～9.0）.Whether the soil is sterilized or not does not affect the degradation of dimethoate in soil.The optimal pH and temperature for degradation were 8.0 and 35℃respectively.The results indicate that strain L3 has potential use in the bioremediation of dimethoate contaminated soil.Studies also found that the dimethoate-degrading enzyme is a constitutive and not inductive enzyme.The best reaction system as following:incubation 30μL crude enzyme in pH7.0 PBS for 30～60min at 30℃,The ion Zn²⁺ could inhibit the enzyme activity.When the concentration of ammonium sulfate precipitation attained to 60%,the enzyme activity of sediment has maximum activity.