Effects of light intensity and light quality on growth and circadian rhythm of saxitoxins production in Cylindrospermopsis raciborskii (Cyanobacteria)

Effects of light intensity and light quality on saxitoxin and neosaxitoxin production by Cylindrospermopsis raciborskii (Woloszynska) Seenaya and Subba Raju (strain T3) were investigated in batch culture conditions. Three light intensities (50, 100 and 150 mu mol photons m(-2) s(-1)) and three light qualities (white and blue 470 nm and red 630 nm) were used. Growth rates were higher under 100 and 150 when compared to 50 mu mol photons m(-2) s(-1) (control condition). Saxitoxin (STX) and neosaxitoxin (NSTX) production showed an increase during the early stationary phase under 50 mu mol photons m(-2) s(-1) (12 days). Higher concentrations of STX and NSTX were observed in cells under 100 mu mol photons m(-2) s(-1). Production of these toxins showed a circadian rhythm synchronized with light:dark (L:D) cycle and also with a period of 24 h under the three light intensities tested. The circadian rhythm of STX and NSTX production under white light conditions was confirmed. Red light induced the loss of circadian rhythm in NSTX production. These data demonstrate a circadian rhythm in saxitoxins production modulated by light.