Studies On Effects Of Quinazoline Derivatives On The Growth Of Microcystis Aeruginosa(Cyanobacteria) And Elucidation For The Mechanisms Under The Effects

Along the deterioration of global water environments，massive cyanobacterialblooms have become a severe environmental problem in freshwaters worldwide.Therefore, developing an effective method to control the cyanobacterial blooms isessential to guarantee the water security and to perform restoration of the aquaticecosystems. Quinazoline derivatives, endowed with a broad spectrum of biologicalactivities and therapeutic properties, had a potential ability to inhibit the growth ofMicrocystis and control the cyanobacterial blooms. In this study，the effects of CMQon M.aeruginosa cultures with both unicellular strain and colonial one, and themechanisms under the effects were examined. The inhibitory effect of CMQ toMicrocystis strains shown in the study suggested that quinazoline derivatives might apotential antialgal chemical.The main results were summarized as follows：1. The growth of M.aeruginosa with both unicellular and colonial strains wereseverely inhibited by CMQ stress. The inhibition rates (IR) of M.aeruginosagrowth exposure to1.25,2.5,5and10mg/L CMQ, were25.82%,58.22%,80.16%and102.16%, respectively. The EC50of CMQ was calculated as1.93mg L-1in a regression analysis “logarithmic-probit” from a computer program,indicating that CMQ was endowed with effective antialgal activities. In theM.aeruginosa colonial strain, the decrease of colonial volume and colonialsettlement were observed under the stress of5and10mg/L CMQ.2. The effects of CMQ on cellular morphology, pigment contents and dissipation offluorescence of M. aeruginosa were shown to be dose dependent. Under the stressof5and10mg/L CMQ, Microcystis cells became swollen wrinkled, transparentand easily broken, and the contents of pigment decreased sharply， and theintensity of fluorescence obviously declined，even to zero. Whereas no significantchanges of cells morphology, fluorescence dissipation and slight increase ofpigments content were shown under the stress of1.25and2.5mg/L.3. The effects of CMQ on the photosystem of M.aeruginosa were exmined. Therewere no significant changes of M.aeruginosa photosystem after exposure to1.25mg/L CMQ. Whereas, the non-cyclic electron flow was slightly inhibited and thecyclic electron flow was enhanced, while PSI and PSII were not affected by 2.5mg/L CMQ. As concentration of CMQ reaching to5and10mg/L, PSI andPSII, the non-cyclic electron flow and cyclic electron flow were all inhibited, asshown by decreasing values of Y(I), Y(II), Y(NPQ), Y(CEF) and ETR(II), andincrease in Y(ND), Y(NA) and Y(NO). The impaired photosystem might lead tothe more heat disspation and the more oxygen radical, and also might inhibit theformation ofATP and NADH, both of which were lethal to M.aeruginosa.4. The expressions of prx, psbA, fabZ and mcyB genes in M.aeruginosa under theCMQ stress were investigated to further prove the physiological results. Byexpsoure to1.25,2.5,5, and10mg/LCMQ for72h, the relative expression levelof prx mRNAs versus control group were1.9,2.5,2.9and5.1times respectively,suggesting that each treatment of CMQ caused the oxidative stress toM.aeruginosa and it was dose dependent. The expression of psbA and fabZ genewere not significantly affected by1.25and2.5mg/L CMQ, however, theexpression was up-regulated when M.aeruginosa was exposed to5and10mg/LCMQ. The relative expression level of psbA mRNAs versus control groupwere3.2and5.2times, and fabZ as1.8and2.1times, respectively. These resultsindicated that the photosystem and cell membranes of M.aeruginosa wereseriously inhibited by higher concentration of CMQ. The microcystin synthesisgene of mcyB was not affected throughout the experiment course.