Estrogenic Effect Of Microcystis Aeruginosa Exudates On Daphnia Magna

Cyanobacteria blooms can release harmful chemicals that disturb the growth and reproduction of other organisms in the water,thus affecting the biodiversity of aquatic ecosystems.Recently,it has been reported that cyanobacteria may interfere with the reproduction of aquatic animals by synthesizing and releasing endocrine disrupter,but the degree of interference,the range of impact,and the mechanism of effect are undefined.Zooplankton plays an important role in the material transformation and energy transfer of aquatic ecosystems.and its response to environmental changes will further affect the stability of the food chain in the water.In order to explore the effects of cyanobacteria on zooplankton reproduction,this study used M.aeruginosa,a dominant species of cyanobacteria as a donor species,the model species of zooplankton Daphnia magna as the receptor.And the initial additive method was used to determine the effect of chronic and acute exposure to M.aeruginosa Exudates(MaE)on the reproductive characteristics,population growth,physiology and biochemistry,gene expression of D.magna.The research contents and results are as follows:(1)In the MaE chronic exposure experiment,Exposed D.magna to 2�104 cells/ml and 4�105 cells/ml MaE,Meanwhile,the non-additive group was taken as the negative control group,Estradiol(E2,10 ?g/l),a representative estrogen at concentrations not less than common environmental levels,was used as a positive control group.Observe for 21 days,compared with negative controls the results shows that two algae density MaE significantly promoted the spawning amount of D.magna,and there was no significant difference in the total number of eggs with 10?g/1 estradiol.It Shows that MaE has a similar effect of estradiol on promoting the spawning process of D.magna.Analyzed the percentage of first reproduction,21 days total number of neonates and promotion rates on neonates,It was found that the total number of neonates for 21 days of D.magna was significantly higher than that in the blank control group,and the two groups of MaE in the reproductive promotion rate were even stronger than the estradiol group.(2)By calculating the innate proportion of increase,finite rate of increase and net reproduction rate showed that MaE not only shortened the growth time of population,but also caused a rapid increase in population and space resources pressure.MaE can also increaing the ability of producing neonates,the growth rate and reproductive potential of the entire population(3)In the proteins and enzymes aspects,by measuring the key protein content and enzyme activity in the reproduction of D.magna at 24h,48h and 96h by acute exposure of MaE.It was found that the content of vitellogenin(VTG)increased significantly at 48h and 96h after MaE treatment(p<0.01).Similarly,the activity of 17?-hydroxylated steroid dehydrogenase(17?-HSD)was significantly enhanced at 48h(p<0.05),and it was extremely significant enhanced at 96h(p<0.01).This suggests that MaE may have stimulated estrogen levels in D.magna and thus enhanced the synthesis of vitellogenin.(4)On the gene expression changes,the expression levels of vitellogenin coding genes(VTG1,VTG2),ecdysone gene CYP314 in D.magna were detected by MaE acute exposure at 48h and 96h,we can find:Under the condition of MaE treatment for 48h,the expression CYP314 and VTG2 gene were significantly down-regulated(p<0.01),and there was no significant change in VTG1 gene(p>0.05).When MaE group were treated for 96h,except for the CYP314 gene,The other two VTG gene were all up-regulated:(p>0.05).The VTG1 gene in the low concentration MaE treatment group was significantly up-regulated(p<0.05).The expression level of VTG2 gene was significantly up-regulated under low concentration of MaE treatment(p<0.05),and extremely significant up-regulated at high concentration(p<0.01).This indicated that the expression of VTG gene encoding vitellogenin in D.magna were promoted by MaE.However,the expression of CYP314 gene,which is related to the synthesis of ecdysone was inhibited.(5)It was also found that the expression of D.magna detoxification gene CYP360A8 treated with estradiol and MaE was significantly down-regulated after 48h treatment,and the detoxification gene was significantly up-regulated at 96h treatment with high concentration of MaE,This indicated that MaE had potential toxic effects on D.magna.The above results reflect the effects of M.aeruginosa on the reproduction of D.magna and the mechanism of action from changes of reproductive characteristics,population growth,proteins and enzymes,gene expression,revealing the potential risk of cyanobacteria to aquatic zooplankton reproduction,It also provides strong support for assessing the ecological hazards of cyanobacteria blooms and provides a scientific basis for corresponding risk prevention.