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

• d-Menthol could inhibit the growth of Microcystis aeruginosa cells effectively.
• After intracellular MCY was released, the concentration of extracellular MCY increased in the medium increased gradually.
• The d-menthol exposure could not degrade the intracellular MCY.

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 × 107, 1.2 × 106, and 2.9 × 105 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.