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

Abstract 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 5 d incubation. After the d -menthol exposure, the dry weight of the cells gradually decreased; the decrease in the dry weight after 5 d exposure was 29, 12, and 2 mg L −1 when the initial cell densities were 1.4 × 10 7 , 1.2 × 10 6 , and 2.9 × 10 5  cell mL −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.