| As the glucose tolerance factor,Cr3+ has the potential function of regulating carbohydrate metabolism.However,the research on the role of Cr3+ in aquatic animals still cannot meet the requirements of its extensive application,and even it may contain enormous hidden risks.Based on this,mud crab Scylla paramamosainas was used as the research object to explore the toxicological and enrichment effects of Cr3+ on S.paramamosainas and its effects on the physiological and biochemical indexes,hepatopancreas transcriptome and intestinal microbiota,etc.Aim to evaluation the comprehensive effect of Cr3+ on S.paramamosainas and accumulate basic data for the application research of Cr3+ in crabs.The main results of this experiment were as follows:1.The LC50 of 24,48,72 and 96 h for Cr3+ to S.paramamosainas were 885.75 mg/L,425.88 mg/L,246.13 mg/L,and SC was 24.61 mg/L,respectively.2.The enrichment and distribution of Cr3+in gills and hepatopancreas of S.paramamosainas were:gills>hepatopancreas;the initial chromium content of gills was(0.983 ±0.117)mg/kg,and the initial chromium content of hepatopancreas was(0.39 ±0.08)mg/kg;Cr3+ was similarly enriched in gills and hepatopancreas of S.paramamosainas.Within 6?9 d of the enrichment test,the enrichment of Cr3+ in gills and hepatopancreas reaches the maximum.After that,except for the hepatopancreas in the 1.25 mg/L group,Cr3+ negative accumulation occurred in all other group.Similarly,except for the gills in the 5.00 mg/L group,Cr3+enrichment plateaus appeared in in all other group;After the enrichment test,the ratio of the chromium content enriched in the gills and hepatopancreas of each group were 4.7,11.0 and 9.1,respectively.3.Low concentration(1.25 mg/L)and middle concentration(2.50 mg/L)of Cr3+could improve the activity of SOD and CAT in hepatopancreas and muscles of S.paramamosainas,and high concentration(5.00 mg/L)of Cr3+could inhibit the activity of SOD and CAT in hepatopancreas and muscles.Cr3+ could increase SOD and inhibit CAT activity in gills.Different concentrations of Cr3+had different effects on the activity of GSH-PX in different tissues.Different concentrations of Cr3+ had opposite effects on T-AOC in the hepatopancreas and gills.The low concentration of Cr3+ will reduce the MDA content in the hepatopancreas and muscle,while the high concentration of Cr3+ would have the opposite effect.Each concentration of Cr3+ would significantly increase the MDA content in the gills(P<0.05).Cr3+can increase the HK and PFK activity in the hepatopancreas of S.paramamosainas and reduce the PK activity.Low concentration of Cr3+ can increase the HK and PFK activity in the muscle,while the middle concentration and high concentration Cr3+ had opposite effects.4.Cr3+could affect the gene expression of the hepatopancreas of S.paramamosainas to a certain extent.Among them,the effect on the middle and high concentration groups were obvious.Significantly differentially expressed genes(P<0.05)were involved in the following metabolic pathways:amino sugar and nucleotide sugar metabolism,glycolysis/gluconeogenesis,glyoxylate and dicarboxylate metabolism,inositol phosphate metabolism and pyruvate metabolism,etc.The analysis of the top 30 significantly differentially expressed genes(P<0.05)with the highest fold difference in each group found that there were only 7 up-regulated genes in the low concentration group and 28 and 29 up-regulated genes in the middle and high concentration groups,respectively.Differentially expressed genes involved in glycolysis and gluconeogenesis-related pathways include:pyruvate kinase,hexokinase,phosphoenolpyruvate carboxykinase,aldolase and fructose-1,6-bisphosphatase 1,etc.,but the differential expression of the above genes was not significant(P>0.05).With the increase of Cr3+ concentration,the expression levels of the above genes are partially down-regulation or down-regulation(P<0.05).The low concentration of Cr3+ would increase the expression level of lactate dehydrogenase,while the effect of middle and high concentration of Cr3+ is opposite.5.The composition of the dominant intestinal microbiota on the phylum of S.paramamosainas includes:Epsilonbacteraeota,Firmicutes,Proteobacteria,Bacteroides,and Fusobacteria.Except for the low-concentration group,the proportion of Epsilonbacteraeota in the intestinal microbiota of each group was the largest.And Arcobacter was the largest genus of Epsilonbacteraeota.By comparing the difference between the intestinal microbiota of the test group and the control group,it was found that Cr3+ could increase the proportion of Fusobacteria in the intestinal microbiota of S.paramamosainas.Low concentration Cr3+ could increase the proportion of Bacteroides,and reduce the proportion of Epsilonbacteraeota,while middle and high concentration Cr3+ had the opposite effect.The metabolic pathways involved in the intestinal microbiota of S.paramamosainas mainly include 13 metabolic pathways such as,amino acid metabolism,carbohydrate metabolism,energy metabolism,lipid metabolism,and nucleotide metabolism.The results of KW rank sum test analysis of the differences in carbohydrate metabolism pathways showed that with the increase of Cr3+ concentration,the abundance of carbohydrate metabolic pathways involved in the intestinal microbiota of S.paramamosainas showed a downward trend,but the difference was no significant(P>0.05).In summary,when the Cr3+ concentration in the water environment was controlled to a lower concentration,it would not have obvious toxic effects on S.paramamosainas,but if it exceeds a certain concentration,Cr3+ would cause the stress response of S.paramamosainas and enrichment in its different tissues and organs.At the same time,the effects of carbohydrate metabolism enzyme activity,hepatopancreas carbohydrate metabolism pattern and intestinal microbiota showed that Cr3+ at this test concentration did not significantly promote the carbohydrate metabolism of S.paramamosainas,but it had a certain effect on its energy metabolism. |
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