Effects of a novel allelochemical ethyl 2-methyl acetoacetate (EMA) on the ultrastructure and pigment composition of cyanobacterium Microcystis aeruginosa.

Allelochemical ethyl 2-methyl acetoacetate (EMA) can significantly inhibit the growth of bloom-forming Microcystis aeruginosa. In order to assess the implication of the damage of EMA on the algal photosynthetic apparatus, the effects of EMA on the algal ultrastructure and pigment composition were investigated. At initial exposure time to EMA (0-40 h), algal allophycocyanin, phycoerythrin and carotenoid degraded firstly; chlorophyll a increased, especially by 47% in the algae exposed to 2 mg L(-1) of EMA; phycocyanin was not significantly affected; lipid bodies increased remarkably. After 40 h of EMA exposure, chlorophyll a decreased gradually, especially by 45% in the algae exposed to 4 mg L(-1) of EMA; lipid bodies greatly reduced but cyanophycin granules accumulated; thylakoid structures were dissolved or disappeared with the presence of numerous vacuoles. These results showed that all ophycocyanin, phycoerythrin and carotenoid were more sensitive to EMA than other pigments, the cells of M. aeruginosa was stressed by EMA with the occurrence of cyanophycin granules and the photosynthesis pigments and ultrastructure of M. aeruginosa were quickly destroyed by EMA with exposure time increasing.