Impact of UV-A and UV-B radiation on growth and toxin production of Nodularia spumigena and Microcystis aeruginosa
Walczak, Agnieszka; Mazur-Marzec, Hanna; Surosz, Waldemar
Stratospheric ozone depletion leads to enhanced UV radiation reaching the Earth. This is why scientific attention is paid to this region of the solar spectrum, which is the most harmful to living organisms. In the present work the impact of artificial UV-A (320 to 400 nm) and UV-B (280 to 320 nm) irradiation on growth and toxin production by two cyanobacterial strains, Nodularia spumigena NSGG-1 and Microcystis aeruginosa PCC7820, was studied. The growth of the species, expressed by both the optical density of the culture and the chlorophyll-a concentration, was measured with spectrophotometry. Analyses showed that the organisms were sensitive to UV-B and, to a lesser extent, to UV-A radiation. With regard to species, N. spumigena was found to be less sensitive to UV in general than M. aeruginosa. Even UV-B irradiation did not inhibit the culture growth as much as in the case of M. aeruginosa. UV seemed to affect the process of toxin production in the tested organisms. Intracellular and extracellular concentrations of hepatotoxins produced by M. aeruginosa (microcystin) and by N. spumigena (nodularin) were analysed with the HPLC method. The results showed that optimal conditions for growth (temp. 21 °C, PAR of 6 W m−2) did not coincide with optimal conditions of toxin production. The concentration of toxins in the culture medium increased with the length of the experiment; the highest concentrations were detected after 24 hours of irradiation with UV-B as well as with UV-A. These findings may shed light on the correlation between growth and toxin production in cyanobacteria exposed to UV radiation.