Effect Of MC-LR And Artificial Floating Beds On The Fish Gut Microbiota

With the development of intensive aquaculture,water eutrophication becomes more and more serious.Frequent cyanobacteria blooms usually take place together with microcystins release,which threaten fish and humans.Artificial floating beds are widely applied due to its effect on water purification and low cost.How the fish gut microbiota accommodates itself and influence the host are not clear until now.3 months old adult zebrafish were exposed to 0,1,5,20 ?g/L of MC-LR for 30 d.We characterized the taxonomic and phylogenetic composition of the bacterial communities using 16 S rRNA pyrosequencing and determined expression of Oatp2b1 and stress related enzyme activities,including superoxide dismutase(SOD),catalase(CAT)and lactate dehydrogenase(LDH).These parameters were further analyzed using linear discriminant analysis effect size(LEfSe)and Spearman correlation test.The availability of artificial floating beds as a way of manipulating gut microbiota was tested by Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis(PCR-DGGE).The results are as follows:After 30 days of treatment with 0,1,5,20 ?g/L of MC-LR,the alpha and beta diversity did not generate significant differences,indicating the existence of a core microbiota,which consisted of Fusobacteria,Actinobacteria,Alphaproteobacteria,Betaproteobacteria,Gammaproteobacteria and other classes.However,db-RDA analysis showed that high dose of MC-LR altered characteristics of high abundances microbiota..The intestine absorbed MC-LR in a dose-dependent manner.Oatp2b1 expression increased with the increasing dose of MC-LR and activities of superoxide dismutase(SOD),catalase(CAT)and lactate dehydrogenase(LDH)increased significantly at low dose and decreased at higher dose.These parameters were further analyzed using linear discriminant analysis effect size(LEfSe)and Spearman correlation test.The identified phylotypes includes Actinobacteria,Lactobacillus and some opportunistic pathogens.Our data highlight the increasing risks of pathogen invasion and recovery tendency via potential probiotics resistance in zebrafish exposed to MC-LR.There existed no significant differences in rhizobacterial composition,and artificial floating beds would not greatly affect the microbiota of pond water.The dominant microbiota in the guts of grass carp changed from Aeromonas jandaei to Paenibacillus sp.Our results indicated that artificial floating beds may serve as a candidate of modulating fish gut microbiota.