The Inhibition Of Compound Allelochemicals On Algae And The Influence On Microcystin Biosynthesis

Serious water eutrophication has led to algal overgrowth and frequentoutbreaks of water blooms, which cause great damage on the function of waterbody and the aquatic ecosystem. Especially, the algal toxins released fromcyanobacteria have been threatening human health seriously. To inhibit the growthof algae by allelochemicals secreted from hydrophyte has become one of theresearch focuses in the field of ecological environment at home and abroad.In this study, inhibition of vetiver oil on Microcystis aeruginosa andScenedesmus obliquus was discussed for the first time, and the mathematicalmodels were established about the inhibition of vetiver oil on those two algaespecies in mixed culture, after then, the composition of vetiver oil was analyzedand identified by GC-MS. In order to find some more effective and cheaperallelochemicals, we selected two kinds of allelochemicals fatty acid that werenonanoic acid and linoleic acid, to investigate and evaluate their joint algaeinhibition, and discussed the possible mechanism for the first time. We alsodiscussed the influence on the content of both intracellular and extracellularMC-RR and the mcyB gene expression when M. aeruginosa PCC7806was underfatty acid stress. The results were as follows:1. Vetiver oil had excellent inhibition on M. aeruginosa （common water bloomcyanobacteria） and S. obliquus （common green algae） in both pure and mixedculture, with more significant effect on M. aeruginosa. The EC₅₀of vetiver oil onthese two algae species in pure culture were0.20and0.30mL L^-1respectively. Theessential component of vetiver oil was sesquiterpenes. The mathematic models ofmixed culture could provide the species densities of M. aeruginosa and S. obliquusat any time point and the concentration of vetiver oil for the best inhibition.2. The mixture of nonanoic acid and linoleic acid had synergistic inhibition onM. aeruginosa. The inhibition ratio of the joint fatty acid on M. aeruginosa was 90.85%, and its EC₅₀was0.0025mL L^-1. The mechanisms of algal cells destructionunder joint fatty acid showed obvious increase of cell membrane permeability andfree radical, however, the activities of the antioxidant enzyme system within cellswere decreased gradually, which was different from the mechanism of the purelinoleic acid on M. aeruginosa. We supposed that the inhibition of joint fatty acidon M. aeruginosa would far surpass the capability of antioxidant enzyme systemwhich could resist the environmental stress.3. Under the joint stress of nonanoic acid and linoleic acid, the expression ofmicrocystin biosynthesis gene B （mcyB） and the intracellular content of MC-RR inunit cells （10⁶cells） of M. aeruginosa PCC7806were increased slightly with nosignificance. Extracellular content of MC-RR was basically unchanged comparedto the control group. There was also no significant difference in the total MC-RR（intracellular and extracellular） between the treatment group and the control group.Since the mixture of nonanoic acid and linoleic acid had synergistic inhibitionon M. aeruginosa, it would not aggravate the algal toxic pollution and could avoidsome problems such as expensive cost by using linoleic acid exclusively andpungent odor emitted from nonanoic acid by using it exclusively. Therefore, themixture of nonanoic acid and linoleic acid could be developed into an efficient,low-cost, environmentally friendly and safe bio-algaecide.