Effects of Different Photoperiods on the Growth of the Cyanobacterium Cylindrospermopsis raciborskii (Woloszynska)

The freshwater Cyanobacterium Cylindrospermopsis raciborskii is potentially toxic and widely distributed in tropical and sub-tropical regions. This species is highly abundant throughout the Anzali Lagoon during the months of July and August. The effects of four different photoperiods (L/D 12:12, 10:14, 14:10, 8:16) on growth rates of C. raciborskii were studied. Cylindrospermopsis raciborskii, isolated from water samples collected from the Anzali Lagoon, was cultured in Zehnder 8 media (using Z8 without a nitrogen source) under light intensity of 3000 Lux at 252oC. A control group cultured with the main culture medium was also used. This experiment was carried out for 25 days. Inoculants and C. raciborskii cells were counted daily throughout the experiment period using a Neubauer chamber and specific growth rates (SGR) and cell division rates (G) were estimated. The maximum growth rate (5±106×8 cells ml-1) was observed at 12L:12D photoperiod followed by 14L:10D, 10L:14D and 8L:16D. The results obtained in the present study especially with 14L:10D and 12L:12D were in complete agreement with general growth pattern of C. raciborskii observed in warmer months with rather longer daytime in tropical and subtropical areas.The strategy of growth in this species may depend on nitrogen fixation, when other algae were nitrogen limited and also ability to grow in low light intensity and high temperature.