Toxicity Effects And Mechanisms Of Typical Toxic Pollutants On Crayfish Procambarus Clarkii

With the acceleration of urbanization and the rapid promotion of industrialization,the impact of industrial wastewater discharge and sudden water pollution on the aquatic ecological environment and human health is increasingly serious.Among the toxic pollutants in water environment,heavy metals,natural toxins and anti-inflammatory drugs are the most common.Among the three types of toxic pollutants,the pollution situations of three typical ones including cadmium(Cd),microcystin-LR(MC-LR)and diclofenac(DCF)are particularly prominent.Due to the increasingly severe environmental problems caused by toxic pollutants in water,their eco-toxicological effects have become one of the major environmental hot issues of global concern.However,there are still many deficiencies in the research on the toxicity mechanisms of toxic pollutants.Based on the above situation,the study on the toxicity mechanisms of the above toxic pollutants on aquatic animals has become a research topic in the field of environmental toxicology.This paper systematically studied the effects of Cd,MC-LR and DCF on the antioxidant defense system,hepatopancreatic transcriptome characteristics,intestinal flora and histopathological changes of the main target organs of Procambarus clarkii,providing theoretical basis for the ecological risk assessment of toxic pollutants in water environment.The oxidative stress response of main target organs including hepatopancreas,gill and intestine of crayfish to toxic pollutants was studied.In Cd exposure experiment,MDA content and the activities of superoxide dismutase(SOD),catalase(CAT)and glutathione S-transferases(GST)in the hepatopancreas of crayfish increased to different degrees,and they reached significant level when crayfish were exposed to different concentrations of Cd for 72 h.In addition,MC-LR and DCF exposure experiments showed that the expression of Mn SOD,CAT,GPx,GST,MT and HSP70 genes showed different changing trends in different organs,suggesting that MC-LR and DCF caused different degrees of oxidative stress and antioxidant defense in the hepatopancreas,gill and intestinal tract of P.clarkii.Meanwhile,the expression levels of different genes related to oxidative stress also changed in different degrees to respond to oxidative stress.The histopathological changes of hepatopancreas tissues exposed to different toxic pollutants were analyzed.The results showed that,when crayfish were exposed to toxic pollutants,there were pathological changes in hepatopancreas,including tubule lumen dilatation and epithelium vacuolization.In the meantime,transcriptome sequencing analysis was carried out on the hepatopancreas of crayfish,including differentially expressed gene screening,GO and KEGG enrichment analysis.It was found that 1061,747 and 1086 differentially expressed genes(DEGs)were identified in 2,5 and 10 mg/L Cd exposure groups,respectively.In 5 and 10 mg/L Cd exposure groups,DEGs were significantly enriched to 5 and 10 GO terms,respectively.In addition,10 mg/L Cd induced significant enrichment of pathways including antigen processing and presentation pathway.In MC-LR exposure experiment,372 and 781 DEGs were identified in 10 and 40 ?g/L MC-LR exposure groups,respectively.In 10 and 40 ?g/L MC-LR exposure groups,DEGs were significantly enriched to 1 and 33 GO terms,respectively.In addition,40 ?g/L MC-LR induced significant enrichment of galactose metabolism pathway.In DCF exposure experiment,642 and 586 genes were significantly differentially expressed in 1 and 10 mg/L DCF exposure groups,respectively.In 10 mg/L DCF exposure group,DEGs were significantly enriched to 12 GO terms.The above three toxic pollutants also caused the abnormal expression of redox-and immune-related genes in the hepatopancreas of crayfish,and then affected redox balance,detoxification,metabolism and immune function.By analyzing the histopathological changes of intestinal tissues,the changes of intestinal tissue structure under exposure to different toxic substances were identified.The results of intestinal histopathological analysis showed that both 5 and 10 mg/L Cd could cause abnormal arrangement of epithelial cells,extension of lamina propria and vacuoles in the microvillis of intestinal tissues.In the meantime,1 and 10 mg/L DCF could also cause similar pathological changes.By contrast,eosinophils(EGCs)appeared in the intestinal tract after MC-LR exposure.Under the condition of 40 ?g/L MC-LR exposure,the muscularis was loose,and lymphocytes infiltrated into the lamina propria.The high-throughput sequencing technology of 16 S r RNA was used to identify the intestinal flora of crayfish and explore the response of intestinal microbial community diversity and structure to toxic pollutants,including Cd,MC-LR and DCF.The results of sequencing showed that Cd,MC-LR and DCF could affect the diversity and composition of intestinal microflora,and change the abundance of intestinal bacteria in different classification levels in crayfish,thus destroying the balance of intestinal microflora,and damaging the function and stability of intestinal microbial community.