Effects Of Silver Nanoparticles On The Metabolites Of Microcystis Aeruginosa

With the rapid development of nanotechnology,influences of nanomaterials on the ecological environment have attracted more and more attention.However,people know little about the effects and mechanisms of nanomaterials on algal metabolites.Here,silver nanoparticles(AgNPs)is selected as the research material,and M.aeruginosa as the model algae.The main purpose of this study is to reveal the effects and mechanisms of the metabolites of M.Aeruginosa under the exposure of AgNPs.The main points are as follows:(1)AgNPs(23±2.92nm)could significantly inhibit the growth of M.Aeruginosa under high concentration(0.15mg/L,0.3mg/L and 0.45mg/L)and showed a"dose-effect",which means that the inhibition effect is enhanced with the increase of AgNPs concentration.Its 96h-half-inhibition concentration(LCso(96h))was 0.13mg/L.The chlorophyll synthesis of M.Aeruginosa was greatly affected by the exposure time and concentration of AgNPs.In short time(24h),AgNPs under high concentration(0.15mg/L,0.3mg/L and 0.45mg/L)could significantly promote the synthesis of chlorophyll of M.Aeruginosa,while AgNPs showed strong inhibition on it in longer time(72h and 96h).It indicates that the inhibition of photosynthesis may be the cause of the toxicity of AgNPs.Silver nitrate had stronger toxic effects than AgNPs under the same amount-of-substance concentration.AgNPs and silver nitrate both had a "hormesis action".It was speculated that the toxicity mechanism of AgNPs and silver nitrate had a certain coincidence.(2)AgNPs under different concentrations(0.075mg/L and 0.150mg/L)and silver nitrate(0.025mg/L)all had great influence on the metabolites of M.Aeruginosa.The differential metabolites mainly consist of alcohols,aerobic acids,fatty acids and other substances.Compared with 0.075mg/L AgNPs,the content of cytochalasin in the metabolites of M.Aeruginosa was higher than that of 0.150mg/L AgNPs,indicating that M.Aeruginosa had stronger stress response to the higher concentration of AgNPs and the effect of AgNPs on the metabolites of M.Aeruginosa was related to the concentration of AgNPs.Differential metabolites mainly included amino acids,oxygen acids,fatty acids and so on.Main metabolic pathways they influenced were the synthesis and metabolism of amino acids and fatty acids,and the metabolism of carbohydrates.Differential metabolites of AgNPs and silver nitrate included pyropheophorbide a,which means that the impact mechanism of silver nitrate and AgNPs on the metabolites of M.Aeruginosa may be similar.(3)The result of transmission electron microscopy(TEM)showed that the effect of AgNPs(0.150mg/L)on the M.Aeruginosa was mainly the influence of its cell morphology and the damage to the thylakoid.Under the action of 0.150mg/L AgNPs,the cell wall of M.Aeruginosa was obviously deformed and damaged,the cytoplasm was deformed and broken,and the cytoplasm showed obvious shrinkage and aggregation,with gas vesicle appearing in the cell.Moreover,AgNPs were widely distributed and aggregated in the thylakoid of M.aeruginosa.It was indicated that one of the possible mechanisms of the effect of AgNPs on the metabolites of M.Aeruginosa was to damage its thylakoid.(4)With the effect of AgNPs under high concentration(0.075mg/L,0.15mg/L and 0.3mg/L),the relative MDA content increased with the increase of the concentration of AgNPs,reaching 1.29 times,2.51 times and 3.05 times higher than that of the control group.When the concentration of AgNPs was 0.15mg/L and 0.3mg/L,the relaive activity of SOD was 2.41 and 2.86 times higher than that of the control group.It suggested that the possible mechanism of the influence of AgNPs on the metabolites of M.Aeruginosa was the oxidative damage and lipid peroxidation.Besides,the effect of silver nitrate on MDA content and SOD activity showed the same tendency,indicating that the impact mechanism of silver nitrate on metabolites of M.Aeruginosa was similar to that of AgNPs.