Effect of different light intensities on the hepatotoxin cylindrospermopsin production by Cyanobacteria algae, Nostoc ellipsosporum

The cyanobacterial bloom leads to the deterioration of the aquatic environment because they release their secondary metabolic to the water, especially toxins. One of the important toxins is Cylindrospermopsin (CYN) which is one of the dangerous toxins that cause liver damage known as hepatic toxin, which poses great health risks to humans. Light plays an important role in the production of these toxins by cyanobacteria through its effect on the photosynthesis process and the gene regulator of these toxins. The current study tested the effect of different light intensities of 26, 52, 78, and 104 mol m^-2 s^-1 on hepatotoxic CYN production by cyanobacterium Nostoc ellipsosporum. The findings of this study showed that the highest inter and extracellular CYN reached 0.047 and 42.5 µg/ml, respectively with a total value of 42.547 µg/ml recorded at the light intensity of 78 µmol photons m^-2 s^-1. The lowest production of intra and extracellular CYN was recorded at the light intensity of 26 µmol photons m^-2 s^-1, which amounted to 0.0006 µg/mg and 7.73 µg/ml, respectively with a total value of 7.735 µg/ml. Also, the highest light intensity inhibited the CYN production which recorded 0.009 µg/mg and 26.39 µg/ml for intra and extracellular contents, respectively, and total production of 26.399 µg/ml. We conclude that light intensity has a vital role in CYN production especially in the optimal condition represented by moderate light, and this effect differs among different cyanobacterial species.