Study On Toxicity And Germicidal Effect Of Polyhexamethylene Guanidine On Eriocheir Sinensis

Polyhexamethylene guanidine(PHMG)is a cationic polymeric disinfectant with a wide bactericidal spectrum,stable and easily soluble in water.In this thesis,the toxicity of PHMG at different concentrations to Eriocheir sinensis larvae and the bactericidal effect of PHMG at safe concentrations were investigated in order to provide a reference for the application of polyhexamethylene guanidine in E.sinensis culture.Firstly,the semi-lethal concentrations of PHMG on E.sinensis larvae were investigated.Based on the 96 h semi-lethal concentration(LC50),the 96 h stress experiments were designed for the blank control,1/10 LC50,1/5 LC50 and 1/2 LC50 concentrations on E.sinensis larvae,and the damage to the gill tissue and hepatopancreas of E.sinensis larvae and the effects on the antioxidant system were investigated by The bactericidal effect on common pathogenic bacteria of E.sinensis at safe concentrations was then examined by quantitative suspension killing assay,and finally the changes in bacterial alpha diversity index and community species at different time periods after the application of PHMG in the water column were examined by high-throughput sequencing method simulating pond conditions.The results of the experiment were as follows:The toxic effects of PHMG on larval E.sinensis were studied.The results showed that the 24 h LC50,48 h LC50,72 h LC50 and 96 h LC50 values were 2.579 mg/L,1.018 mg/L,0.847 mg/L and 0.796 mg/L for the larvae of E.sinensis,respectively.The results showed that after 96 h of exposure to PH MG concentrations of 0.080 mg/L,0.159 mg/L and 0.398 mg/L,the hepatopan creas and gill tissues of E.sinensis larvae in the low PHMG treatment group(0.080 mg/L)were not significantly different from those in the control group,while those in the medium PHMG treatment group(0.159 mg/L)were not significantly different from those in the control group.The hepatopancreas and gill tissues of E.sinensis larvae in both the medium(0.159 mg/L)and high(0.398 mg/L)PHMG-treated groups showed significant tissue damage and lesion characteristics.Treatment of E.sinensis larvae with different concentrations of PH MG increased the antioxidant enzyme activities of E.sinensis larvae.After 96 h of stress,the index of antioxidant enzyme activities increased,the total antio xidant capacity decreased and the antioxidant system was damaged in the medium(0.159 mg/L)and high(0.398 mg/L)PHMG-treated groups;the total antiox idant capacity of the low PHMG-treated group(0.080 mg/L)showed no significant difference(P>0.05)in total antioxidant capacity and no significant difference(P>0.05)in antioxidant enzyme activity index of hepatopancreas and significantly higher(P>0.05)in antioxidant enzyme activity index of gill tissue than the control group.The bactericidal effect of different concentrations of PHMG on the major pathogenic bacteria of E.sinensis was studied.The bactericidal rates of different concentrations of PHMG against the major pathogenic bacteria of E.sinensi s,including Vibrio alginolyticus,Vibrio parahaemolyticus,Morganella mori,Ed wardsiella retardans,Aeromonas hydrophila,Aeromonas vivax,Escherichia coli and Staphylococcus aureus,were investigated using the quantitative bacterials uspension killing assay.The bactericidal log values(KL)of PHMG against Vib rio parahaemolyticus,Edwardsiella retar dans,Aeromonas hydrophila,Aeromonas vivax,Escherichia coli and Staphylococcus aureus were all greater than 5,in dicating that PHMG had a good killing effect on the major pathogenic bacteria of E.sinensis at PHMG concentration of 0.080 mg/L.The effectiveness of PHMG(0.080 mg/L)in sterilising simulated pond waters was examined.The changes in bacterial alpha diversity index and community species in the water column after the addition of PHMG were examined by high-throughput sequencing.The results showed that the addition of PHMG altered the community structure of bacteria in the water column and substrate,with a significant decrease in the alpha diversity index(P<0.05).The relative abundance of Proteobacteria in the water column was significantly higher(P<0.05),the relative abundance of Actinobacteria was significantly lower(P<0.05),the relative abundance of Proteobacteria in the substrate was significantly higher(P<0.05)and the relative abundance of Phylum Firmicutes was significantly higher(P<0.05).In summary,the safe concentration of PHMG for juvenile E.sinensis is 0.080 mg/L.This concentration of PHMG has a good bactericidal effect on the main pathogenic bacteria of E.sinensis,and when applied to the water column,it reduces the alpha diversity index of bacteria in the water column and changes the community structure of bacteria.