Ecotoxicity Of Hydrogen Peroxide On Microcystic Aeruginosa:Effect Of Growth Stage And Role Of Cytochromes P450

Cyanobacterial bloom has been rising as a worldwide issue owing to its adverse effects to water quality and ecological health.The efficient prevention and control of pollution is the direction of the researchers' efforts.To solve this problem,hydrogen peroxide?H₂O₂?has been considered as a potential algaecide because no by-products are generated after treatment.Previous investigations have concentrated more on logarithmic phase of cyanobacteria but less about growth indexes and characteristics of algal cells at different growth stages.Therefore,it is of great significance to study the properties of different growth stages and to control cyanobacteria in a targeted way.In addition,cytochromes P450?CYPs?was reported to be related with H₂O₂,but the roles of CYPs in the regulation of H₂O₂ in cyanobacteria have yet to be investigated.In this study,the CYPs suicide inhibitor 1-aminobenzotriazole?ABT?was added to the representative cyanobacteria Microcystis aeruginosa?M.aeruginosa?exposed to H₂O₂.The properties of algal cells at different growth stages and the roles of CYPs in the regulation of H₂O₂ in cyanobacteria were investigated and related mechanism was also discussed.The main conclusions of this research are showed as followed.?1?The division and research of different growth stages:The early stage?0-4 d?,the number of cells is the less,and the consumption of H₂O₂ is less.Although there were algal cell breakage and toxin release,it would be degraded by H₂O₂,and the residual toxin is less than that of other stages.Logarithmic phase?5-16 d?:Cell grew rapidly and the consumption of H₂O₂ was the largest;cell growth was inhibited under H₂O₂ but cell integrity was influenced slightly.In this stage,a large number of algal toxins were still being released after treatment.Stable period?17-36 d?:algal cell integrity was seriously damaged,at the same time H₂O₂ degraded part of the toxin.While considering the stable period has the maximum number of cells,there was a large number of toxins outflow to the water after treated with H₂O₂.The decline period?after 37 d?:The number of cells in this stage is less,most of the cells are destroyed,and H₂O₂ was mainly acts on broken cell debris or other substances in the water body.Therefore,in conclusion,the selection of cyanobacteria in the initial stage of growth will more economical and efficient.?2?The results showed that CYPs mediates the effects of H₂O₂ on M.aeruginosa.To be exact,the addition of ABT induced greater inhibitory effects on the growth and higher reactive oxygen species levels in M.aeruginosa comparing to those treated with H₂O₂ alone.At the same time,photosynthetic parameters significantly decreased,and photosynthetic genes?psaB,psbD1 and rbcL?decreased,confirmed the effects on the electron transport of photosynthesis.In summary,P450 enzyme plays a mediating role in the effect of H₂O₂ on growth inhibition,ROS and photosynthesis of Microcystis aeruginosa.?3?The H₂O₂+ABT group was compared with the H₂O₂ group:the microstructures of Microcystis aeruginosa cells showed obvious changes.The structure of cells was disordered.The thylakoid has an irregular fracture,the cytoplasm color becomes shallow,and the separation of the wall was obvious.In addition,the content of extracellular microcystins-LR?MCLR?increased but the total MCs decreased.ABT also intensified the aggregation of Fe,which might explain the effects on photosynthesis and synthesis of MCLR.Furthermore,the transcriptional levels of MCs-synthesis genes?mcyA and mcyD?decreased but MCs-release gene?mcyH?increased,which confirmed the effects on the MCLR production/release.In conclusion that P450 enzyme plays a mediating role in the effect of H₂O₂ on microstructure,distribution of Fe protein and MCLR production/release of Microcystis aeruginosa.In summary,this study illuminated the the properties of algal cells at different growth stages and the mediation role of CYPs in the adverse effects on M.aeruginosa induced by H₂O₂,thus providing new theoretical basis for the explanation of H₂O₂ as potential algaecide.