Study On The Inhibitory Effect Of Water Blooms Cyanobacteria By Flavonoids

Cyanobacterial blooms have posed great threaten to water environment and human health,and flavonoids as allelopathic substances received great attentions for their remarkable ability of inhibiting harmful algae blooms(HABs).In this study,some typical flavonoids were selected to test their inhibitory effects on the dominant species in the cyanobacteria bloom,i.e.Microcystis aeruginosa and Planktothrix agardhii.We tried to explain how the structural characteristics of flavonoids affect the activities of HBAs inhibition,and then explore the mechanism of inhibition by biochemical analysis to provide theoretical instruction for the application of flavonoids in the inhibition of cyanobacteria bloom.The main results of this study were summarized as follows:1)A11 of the eight flavonoids tested in this study showed a significant inhibitory effect on the growth of Microcystis aeruginosa,and the inhibitory effect is enhanced with the increase of the concentration.The inhibition rate of the different flavonoids was different from each other.The inhibitory abilities of the tested flavonoids ranged from weak to strong were chrysin<galangin<apigenin<baicalein<quercetin myricetin<kaempferol<luteolin.Especially luteolin and kaempferol could show a more than 75%inhibition rate of Microcystis aeruginosa at the concentration of 10 mg·L-1.The inhibitory effect of flavonoid glycosides was better than the aglycones(count as ?M).2)The number and location of hydroxyl groups of flavonoids had great influence on the algae inhibition effect.The flavonoids with four hydroxyls showed the best inhibition activity.When the total number of hydroxyl groups is small,the presence of 3-OH could enhance the inhibition ability but when the total number of hydroxyl groups is large,the presence of 3-OH will weaken the inhibition ability.The flavonoids with 4'-OH showed good anti-algae properties,and with the increasing of the number of hydroxyl groups on the B ring,the inhibition ability of flavonoids enhanced,but the flavonoids with a structure like pyrogallic acid show not so well in inhibition as they were too easy to be oxidized.The presence of 6'-OH can also enhance the activity.3)Flavonoids had good inhibitory effects on not only Microcystis aeruginosa,but also Planktothrix agardhii.The inhibitory effect of the same compound on the growth of Planktothrix agardhii was a little bit weaker than that of Microcystis aeruginosa,but the difference is not so signifintly.It can be concluded that flavonoids had the potential of becoming an efficient and broad-spectrum inhibitor in fighting against HABs,but attentions should be pay to avoid the releasing of algal toxins as secondary pollution.4)Flavonoids may inhibit the growth of cyanobacteria by affecting the photosynthetic system,the antioxidant system or destroying the cell membrane.The existence of flavonoids reduced the content of chlorophyll a in the cell of cyanobacteria,inhibited the electron transport process of photosynthesis,and decreased the utilization of photosynthetic rate;low concentration of flavonoids could stimulate the antioxidant system of cyanobacteria,leading to increased activity of CAT and SOD in cyanobacteria cells;low concentrations of flavonoids could increase the content of MDA in cyanobacteria,but as the concentration of flavonoids increased the algal cells turned to die and the level of MDA decreased.