| Microcystis aeruginosa was overspreading all over the world, with increasing water bodies of eutrophication. The heptapeptide compound produced by single cell cyanobacteria not only caused human liver cancer, but also affected regular growth of aquatic plant and animal, at last leaded to the serious ecosystem unbalance. Therefore, harness of the "ecology cancer" was taken seriously by many countries in recent years. In spite of substantive investments expenditure and abundant research work, breakthrough development has not been made as yet.The research purpose was aimed to explore a novel approach about biological control Microcystis. So far methods for countering the growth of M. aeruginosa described in recent publications can be conventionally subdivided into physicochemical, chemical, and biological control which was deemed to the most promising method. In biological control, animal, plant, and microbial technology were already applied, plant technical especially was superior because of lower cost and fewer sequela. There were two types of phytogenic technique, higher plant and algae (microalgae). The method of higher plant inhibiting Microcystis was effective, but their limited growth range and lower growth rate made application area narrow. With studies on algae allelopathy developed, some researchers suggested this may be the effective approach to solve harmful algae blooms lately. The definition of Allelopathy include any process involving secondary metabolites produced by plants, algae, bacteria and fungi that influenced the growth and development of biological and agriculture systems. In the recent decade, many studies have already been done on higher plants and algae. But using allelopathic effect of microalgae to inhibit growth of Microcystis has not been reported as yet.By a chance, we have discovered that one species of Eukaryotic alga can inhibit Microcystisgrowth effectually. For this phenomenon, we have done further research from the following four aspects: (1) Mix cultivation of the Eukaryotic alga and Microcystis in different medium; (2) Microcystis cultivation in the cell-free filtrate medium of the Eukaryotic alga; (3) photoperiod, pH and temperature regulated the allelopathy from Eukaryotic alga; (4) mechanism of Eukaryotic alga allelopathy inhibiting Microcystis growth.The data suggested: (1) in low temperature(24°C)culture, Eukaryotic alga can inhibit Microcystis growth in BG11 and MA medium, and the inhibition of Eukaryotic alga can't be impacted by nutrition and strain difference. (2) In BG11 and MA medium, the cell-free filtrate of Eukaryotic alga inhibited Mcrocystis growth, it means that Eukaryotic alga this inhibition of the growth of Microcystis may from allelopathy. (3) Temperature, pH and illumination regulated the allelopathy from Eukaryotic alga. In culture system, the inhibition ability of allechemical depend on integral result of the above several factors. In this experiment, the optimum conditions for the allelopathy were as follows: the temperature was lower than 30°C, the pH was about 6.5 and the illumination time was 14h. Allechemical produced by Eukaryotic alga may be organic substance. (4) Action mechanism of allelopathy from the Eukaryotic alga may affect photosynthesis and the gene expression related with Microcystis cell division.These data were practically significant in biology control reproduction of Microcystis, insuring drink quality and protecting human health. The next work should be isolate and identify allechemical properties and structure furtherly, open a way to use the allechemical and this may be explain regulation mechanism of Microcystis cell division.
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