| Enrofloxacin?ENR?,a fluoroquinolones antibiotic,is widely used in medical and aquaculture fields.It's one of the antibiotics with more residues in the surface waters in China,which has a serious impact on the health of water ecosystem.However,there are few studies on both its toxicity to microalgae or microorganisms and the degradation or removal by microalgae or microorganisms in water.In this study,we used six freshwater microalgae,Dictyosphaerium sp.?FACHB-1902?,Scenedesmus quadricauda?FACHB-1471?,Chlorella vulgaris?CFWA02010?,Microcystis aeruginosa?CFWA01001?,Synechococcus elongatus?CFWA01023?,and Chrysosporum ovalisporum?CFWA01009?as objects,through laboratory simulation experiments,to analyze the changes in the growth,photosynthetic activity and response of exopolysaccharides?EPS?of six microalgae under the exposed of different ENR concentrations and the removal rate of EN R by microalgae.To filter the microalgae which has higher removal ability of EN R,heating to extracted its EPS,by adding different proportions or concentrations to explored the role of EPS in the process of removing EN R from water by microalgae and microorganisms.In order to:?1?Provide new insight for the understanding of the ecological toxicity of fluoroquinolones antibiotics to primary producers in aquatic system;?2?Provide new ideas for the ecological removal of antibiotic residues in water bodies and the biological resource utilization of freshwater microalgae.The main research results are as follows:?1?In each treatment group with different concentrations of ENR,the biomass and photosynthetic pigment content of the three green algae had increased with the increasing of culture time.But the three types of cyanobacteria were opposite,and compared with the antibiotic-free control group,ENR has significantly inhibited the growth and pigment accumulation of six microalgae?P<0.05?.Besides,ENR can stimulates microalgae to release EPS,The content of water-soluble polysaccharides?RPS?and extracellular gum sheath polysaccharide?CPS?of several microalgae generally increased with the increase of ENR concentrations.On the 12th day,the removal rates of 5 to 100 mg·L-1 ENR in the treatment groups with Dictyosphaerium sp.were 3.21,3.01,2.69,and 2.83 times than that of the control group?algae-free group?.Compared with groups without microalgae?control?,all six microalgae had significant promotion effect on the removal of ENR at different concentrations?P<0.05?.Comprehensively speaking,Dictyosphaerium sp.,Scenedesmus quadricauda and Chrysosporum ovalisporum had high removal rate of ENR than that other three microalgae.?2?Adding different proportions of Dictyosphaerium sp.EPS extracts to Dictyosphaerium sp.,Scenedesmus quadricauda and Chrysosporum ovalisporum for experiments.To investigate the role of microalgae EPS in microalgae growth and ENR removal under 25 mg·L-1 ENR exposure.It was found that compared with the control group,the microalgae EPS can increase the biomass of the three microalgae,and at the same time,it can significantly promote the cytochrome accumulation and photosynthesis of Dictyosphaerium sp.and Scenedesmus quadricauda?P<0.05?,but it has inhibitory effect on Chrysosporum ovalisporum.Adding Dictyosphaerium sp.EPS can inhibit the synthesis and release of RPS and CPS from microalgae.The higher of EPS added,the lower of the RPS,CPS and catalase activities?C AT?of the three microalgae,indicates that the degree of stress by ENR has been alleviated.The ability of three microalgae to remove 25 mg·L-1 ENR under the same culture conditions was shown as Dictyosphaerium sp.>Chrysosporum ovalisporum>Scenedesmus quadricauda,compared with the control group,the EPS has a significant promotion effect on ENR removal by microalgae?P<0.05?.?3?Take water samples from Minghu Lake of Shanghai Ocean University for pretreatment,then added the different proportions EPS of Dictyosphaerium sp.and Synechococcus elongatus to culture microorganisms,to studied the role of EPS in the removal of ENR by microorganisms.It was found that during the culture period,the p H of the culture solution gradua lly increased,and the higher of the microalgae EPS addition,the higher of the p H,but each treatment group was lower than the control group during 16 days.The content of RPS in each group was at a low level within 8days,and rose rapidly after 8 days.Analysis and comparison of the relative abundance of microorganisms in each group found that the microbial diversity and community characteristics changed during the experimental period.Betaproteobacteriales,Frankiales,Bacillales and Synechococcales were bominant species in 0 day,mainly were Sporichthyaceae,Burkholderuaceae,Gemmataceae and C yanobiaceae,etc.On the16th day,the relative abundance of Betaproteobacteriales increased significantly,and Verrucomicrobiales and Microtrichales also account for a large proportion,mainly were Verrucomicrobiaceae,Burkholderuaceae,Ilumatobacteraaceae and Reyranellaceae,etc.ENR and EPS promoted the increase in microbial?lpha diversity?Shannon index?,PCo A analysis of?diversity also showed that EN R and EPS had important effects on the stability of microbial community structure.Compared with the control group,microalgae EPS can directly promote enrofloxacin removal,and can also increased the ENR removal buy affecting changes in microbial dominant flora.C yanobacteria EPS is more obvious effect than that green algae,and the removal rate can reached 19.90%. |
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