Inhibitory effects of plant-produced phenols on algal growth

Abstract

Evaluated here are the inhibitory effects on blue-green algae (Microcystis aeruginosa) induced by nine plant-produced phenols (caffeic, p-coumaric, ferulic, protocatechuic, sinapic, syringic, and vanillic acids, catechol, and hydroquinone), two plant-produced acids (quinic and shikimic acids), phenol, resorcinol, hydroxy hydroquinone, and phloroglucinol. Algal assays confirmed the growth inhibition of M. aeruginosa by polyhydric phenols, i.e., caffeic/protocatechuic acids, catechol, hydroquinone, hydroxy hydroquinone, and phloroglucinol, and by phenols containing methoxy groups, i.e., sinapic and syringic acids. Accordingly, this indicates the great feasibility of controlling the growth of M. aeruginosa using such plant-produced polyhydric phenols and/ or phenols as additives. A comparison of the inhibitory effects of the polyhydric phenols showed that those induced by polyhydric phenols in which phenolic hydroxy groups bound a benzene ring at ortho- and/or para-positions to another phenolic hydroxy group are stronger than the effects induced by polyhydric phenols in which phenolic hydroxy groups are at only meta-positions. Experiments showed that the only polyhydric phenols demonstrating significant growth inhibition of M. aeruginosa were autoxidized. Based on the observed life times of radicals produced by autoxidation of pyrogallic/gallic acids and the relationships between the autoxidation times of these polyhydric phenols and their algal growth inhibitory effects, it was hypothesized that such radicals and other autoxidation products inhibit algal growth and that the autoxidation products must play quite important roles.