RESPONSES AND RESTORATION OF THE WATERBLOOM-FORMING CYANOBACTERIUM MICOCYSTIS AND A GREEN ALGA CHLORELLA UNDER DARKNESS AND LOW TEMPERATURE

The growth, pigment content, maximum variable fluorescence (F_v/F_m), malondialdehyde (MDA) content, and antioxidant enzyme activity were investigated in Microcystis aeruginosa PCC 7806 and a green alga, Chlorella sp. FACHB-31, which were cultured under darkness and at a low-temperature in the present study. After a 30-d incubation under darkness and at a low temperature, chlorophyll a showed a significant decrease and the carotenoid unit content significantly increased in Microcystis and Chlorella. The MDA content and catalase (CAT) activity exhibited significant changes in Microcystis, while MDA content and CAT activity in Chlorella did not change markedly. Additionally, the survival rate of Microcystis was 54.6%, which is higher than that of Chlorella (31.3%). When returning to normal temperature and illumination, both algae showed a rapid growth. These results suggest that Microcystis survived by reducing its metabolic activity, but that Chlorella maintained a stable high metabolic activity under dark, low temperature winter conditions.