Effects of d-menthol stress on the growth of and microcystin release by the freshwater cyanobacterium Microcystis aeruginosa FACHB-905.

The effects of d-menthol on the growth of Microcystis aeruginosa FACHB-905 and microcystin (MCY) concentration were evaluated by batch culture experiments. The algal biomass and the intracellular and extracellular MCY concentrations were evaluated during 5d incubation. After the d-menthol exposure, the dry weight of the cells gradually decreased; the decrease in the dry weight after 5d exposure was 29, 12, and 2mgL(-1) when the initial cell densities were 1.4×10(7), 1.2×10(6), and 2.9×10(5)cellmL(-1), respectively. The results indicate that the d-menthol exposure inhibited the cellular growth, thus also inhibiting the increase of the total MCY concentration. In the presence of d-menthol, the intracellular MCY was gradually released into the medium after the cell lysis. The extracellular MCY concentration in the medium was significantly higher in the d-menthol-exposed samples than in the control samples, confirming that d-menthol cannot decompose the extracellular MCY.