Biocidal effect of (E)-anethole on the cyanobacterium Aphanizomenon gracile Lemmermann

Biocidal natural substances of botanical origin offer a promising ecofriendly option for controlling toxic cyanobacteria. Herein, we study 11 essential oils and some of their major components for their activity on Aphanizomenon gracile . On the basis of our results we support that Origanum vulgare and O. dictamnus , Ocimum basilicum , Eucalyptus meliodora , Melissa officinalis , and Pimpinella anisum exhibited the strongest activities, and the IC 50/1d values of the extracts were calculated to be between 168.43 and 241.97 μg mL −1 . When the major components of the biocidal essential oils were tested individually, ( E )-anethole was found active, exhibiting an IC 50/1d value of 71.35 μg mL −1 . On the other hand, the half-life ( t 1/2 ) of ( E )-anethole was calculated at 1 h. A preliminary attempt of ( E )-anethole microencapsulation was conducted, in order to slowly release this biocidal agent, increasing the residual life under open air conditions and thus the biological activity. Results were promising since the microencapsulated product exhibited better activity than did the non-formulated ( E )-anethole. This is a first report on the biocidal activity of EOs and ( E )-anethole on A. gracile and a preliminary indication of the microencapsulated ( E )-anethole potential use as a natural biocidal in fresh waters. Graphical abstract Filaments of Aphanizomenon gracile capable of bloom forming (strain SAG 31.79, in a batch culture) and ( E )-anethole