Myriophyllum spicatum-released allelopathic polyphenols inhibiting growth of blue-green algae Microcystis aeruginosa

A culture solution of macrophyte Myriophyllum spicatum was subjected to algal assay-directed fractionation on the basis of polarity and molecular weight. As the water-soluble fraction below molecular weight 1000 was the only fraction to inhibit the growth of blue-green algae Microcystis aeruginosa, it was analyzed by analytical high-performance liquid chromatography (HPLC) and atmospheric pressure chemical ionization mass spectrometry (APCI-MS) in order to identify M. spicatum-released growth-inhibiting allelochemicals. Both HPLC and APCI-MS revealed the release of four polyphenols exhibiting growth inhibition effects, i.e., ellagic, gallic and pyrogallic acids and (+)-catechin. A quantitative investigation of their respective inhibitory effects showed that (1) gallic and pyrogallic acids are more inhibitory than (+)-catechin and ellagic acid, and that the autoxidized products of each polyphenol demonstrated growth inhibition. Finally, when the collective activity of a mixture of the polyphenols was examined, synergistic growth inhibition of M. aeruginosa occurred.