Toxicity Of Deltamethrin To Juvenile Chinese Mitten Crab And Application Of Pesticide-degrading Bacteri

Pyrethroid is a synthetic biomimetic compound,which is widely used in the control of agriculture,animal husbandry and daily household pest.Deltamethrin,high efficiency cyhalothrin,cypermethrin and bifenthrin are the most common pyrethroid pesticides in the market.In recent years,deltamethrin is one of the fastest-growing and most toxic species among them.Many aquaculture farmers of Chinese mitten crab Eriocheir sinensis use deltamethrin to remove wild fish and pests,even used to clear ponds.Thus,the growth and quality of E.sinensis were affected in the process of culture.As the main way of bioremediation,microbial remediation plays an important role in the degradation of pesticide residues.Therefore,it is of great significance to study the toxicity of deltamethrin on E.sinensis and to find effective degrading bacteria.In this paper,the toxic effect of deltamethrin on E.sinensis was studied.A highly efficient degrading bacterium P-2 was isolated from the sediment of cultured pond.The degradation efficiency of the strain was verified in the culture of E.sinensis.The results are as follows:（1）The sensitivity of E.sinensis to deltamethrin was studied from two aspects of morphology and immunology.The toxicity of the pesticide to E.sinensis at 24h-LC₅₀,48 h-LC₅₀,96 h-LC₅₀was 6.5,5.0,2.75μg/L,respectively,and the safe concentration was 1.2μg/L.The concentrations of 1/2,1/5 and 1/10 of 96h-LC50（1.37,0.55 and 0.28μg/L）were added in the experimental groups.Changes of enzyme activity and gene expressions of SOD,CAT,MDA,PO in hepatopancreas of E.sinensis were measured at 1,3,6,10,15 d after deltamethrin stress.In addition to the content of MDA,enzyme activity and gene expressions showed a tendency to increase and then decrease,reaching the maximum at the 6th-10th day of stress.The content of MDA accumulated with the increase of stress time.After 15 d of deltamethrin stress,the hepatopancreas of E.sinensis were damaged.Compared with the normal crab hepatopancreas,the number of B cells decreased abruptly,a large number of vacuoles appeared,the basement membrane was separated from the epithelial cells,and flocs appeared in the lumen.The results showed that E.sinensis was highly sensitive to deltamethrin.With the increase of stress time,the immune system and the hepatopancreas structure were destroyed.（2）From the sediment of E.sinensis culture pond which used deltamethrin for clearing bottom sediment,a candidate strain of deltamethrin-degrading bacteria P-2 was isolated.Through morphological observation,physiological and biochemical identification as well as sequence analysis of 16s r DNA gene,it is concluded that the strain belongs to Paracoccus sp.（3）The degradation characteristics of the strain were analyzed by controlling single factor variables,including inoculum amount,p H value and initial concentration of pesticide.The results showed that when p H was 7,the substrate concentration was small,the inoculation amount was large,and the degradation effect of the strain was good.The degradation efficiency of 100 mg/L deltamethrin was up to 86.6%within 5days by using P-2.（4）The degradation of deltamethrin was tested under laboratory culture conditions.In the culture water of E.sinensis,the initial concentration of deltamethrin was 3.0μg/L.And then the isolated degrading bacterium P-2 was added.The concentration of P-2 in the water is 6.0×10⁸CFU/L.The results showed that the deltamethrin residue in hepatopancreas and muscle tissue of E.sinensis decreased significantly in the experiment group.The degradation rate can reach 80%in hepatopancreas and 72%in muscles.At present,the maximum residue of deltamethrin in fish is 0.03 mg/L.The residue of edible part of E.sinensis was much lower than the above standard.The results showed that strain P-2 could effectively reduce the residue of deltamethrin in E.sinensis.