Abstract
Myriophyllum spicatum is known to cause allelopathic growth inhibition of a cyanobacterium Microcystis aeruginosa. This study was carried out to identify unknown allelochemicals released from M. spicatum and to investigate their anti-cyanobacterial effects.
A fraction containing unknown allelochemicals was obtained by the fractionation of a culture solution of M. spicatum using high performance liquid chromatography. A series of analyses of its culture solution and methanol extract using gas chromatography mass spectrometry revealed that fatty acids, i. e. nonanoic, tetradecanoic, hexadecanoic, octadecanoic, and octadecenoic acids were released by M. spicatum. Nonanoic, 6-cis-octadecenoic, and 9-cis-octadecenoic acid significantly inhibited the growth of M. aeruginosa, while tetradecanoic, hexadecanoic, octadecanoic acids did not show any effect. Comparing the inhibitory effect of nonanoic acid with those of the four polyphenols and eugeniin which were previously reported as M. spicatum-released anti-cyanobacterial compounds, nonanoic acid was found to be most inhibitory to M. aeruginosa. In addition, nonanoic acid and pyrogallic acid, one of the M. spicatum-released anti-cyanobacterial polyphenols, caused synergistic growth inhibition of M. aeruginosa. These results indicate that not only polyphenols and tannins but also fatty acids such as nonanoic acid must be studied to reveal how M. spicatum causes its allelopathic effect on M. aeruginosa.
