A Study On The Toxicity Effect Of Microplastics/tetracycline Complex On Button Polyps

Coral reefs,one of the marine ecosystems,play an essential role in fishery resources,pharmaceutical developments,culture tourism and coastal zone protection.In recent years,coral reefs have also been identified as an important potential blue carbon sink for mitigation climate change.Microplastics(MPs),a new type of pollutant,are the plastic fragments with a size less than 5 mm.MPs are easy to absorb organic pollutants such as antibiotics and pesticides in the marine environment due to their small volume and large specific surface area.Up to now,the death of coral caused by MPs and the transmission of resistance genes and the generation of drug-resistant bacteria caused by antibiotics in coral reefs have been reported,but the toxicity effect of the microplastics/tetracycline complex on coral reefs have never mentioned.Based on this background,this study investigated the toxicity effect of three different types of MPs on button coral in terms of behavioristics,symbiosis,key metabolites and enzyme activity.Moreover,16 S r DNA sequencing and transcriptomics were employed to explore the damage mechanism,which provided data and theoretical support for the impact assessment of MPs and microplastics/tetracycline complexes on button coral.The main research contents and results are as follows:(1)Toxicity effect of different types of MPs on button coral.This part aimed to assess the toxicity effect induced by the presence of three types of MPs,namely,polyvinyl chloride(PVC),polyethylene(PE),and poly(methyl methacrylate)(PMMA),on button polyps(Protopalythoa sp.)after short(96 h)-and long(28 day)-term exposure.The results showed that MPs can adhere to the coral surface and enter the coral body,which causes coral to secrete mucus and lose symbiotic zooxanthellae.The results indicated type-and time-dependent cytotoxic effects of MPs.On short-term exposure,the MPs cause the corals to produce a mass of peroxides,which also initiate their immune and detoxification systems.After long-term exposure,the immunocompetence,photosynthetic efficiency,and oxidation resistance of corals were damaged to various degrees by MPs.(2)Kinetics of tetracycline adsorption on different types of MPs.PE,PVC,PMMA were used to adsorb tetracycline at low concentration(1 ?g/L)and high concentration(10 ?g/L),respectively.The results showed that all the adsorption processes reach adsorption equilibrium at 24 h,and the adsorption amount was correlated with the concentration of TC.The adsorption results conformed to the pseudo-first order adsorption kinetics model.(3)Effects of microplastics/tetracycline complex on symbiotic microorganism of button coral.Three kinds of MPs(PE,PVC,PMMA)were mixed with low concentration(1 ?g/L)and high concentration(10 ?g/L)TC,respectively.This part studies the effects of complex on the symbiotic microorganism of button coral.The results showed that MPs could significantly increase the diversity and richness of symbiotic microorganism of button coral.The effect was enhanced with the increase of TC concentration of complex.Short-term exposure to low concentrations of MPs and tetracycline did not change the composition of dominant species in button coral,but decreased the abundance of dominant species.MPs and tetracycline can cause changes in the abundance of some important functional species of button coral at the genus level,For example,PE and PVC resulted in an increase in Endozoicomonas,while tetracycline decreased the abundance of Sphingomonas.In addition,MPs and complexes alter the community structure of symbiotic microorganism in button corals.(4)Effects of microplastics/tetracycline complexes on gene expression of button coral.Differential gene expression analysis showed that MPs could affect the gene expression of corals,and the degree of influence was as follows : PVC>PMMA>PE.KEGG pathway enrichment analysis showed that PE mainly affected the synthesis pathway of ribosomes in button coral.PMMA affects ribosomal protein pathway,arginine biosynthesis pathway,amino acid biosynthesis pathway and so on.PVC can significantly up-regulate the ABC transporter system and significantly down-regulate the ECM receptor interaction pathway and metabolism of button coral.Tetracycline can cause the disorder of various amino acid metabolism and vitamin synthesis pathway in button coral.In addition,this study selected PVC and PVC/TC group for trend analysis.With the increase of TC concentration,the pathways of glutathione ATPase,heat shock protein HSP90 and isocitrate dehydrogenase were up-regulated larger,while the level of Rad50 ATPase,green fluorescent protein and acetylcholinesterase were negative related to TC concentration.In summary,these results suggest that PVC can affect the processes of fluorescence protein synthesis,oxidative stress,DNA damage and energy metabolism of button coral.