Physiological Responses and Toxin Production Of M. Aeruginosa in Short Term Exposure to Solar UV Radiation.

HERNANDO M; ROSSO L; MALANGA G.; HOUGHTON C; GIANNUZZI L; SEDAN D; ANDRINOLO D

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

Due to stratospheric ozone depletion, several organisms will become exposed to increased biologically active UVB radiation (UVBR, 280?315nm), not only at polar but also at temperate latitudes. In order to evaluate the effects of UV radiation (UVR, 280-400nm) on physiological responses and toxin production of a native Microcystis aeruginosa (strain CAAT 2005-3 [1]), three radiation treatments (by using different filters) were implemented: (i) P (PAR, 400-700nm), (ii) UVA (PAR+UVAR, 315-700nm) and (iii) UVB (PAR+UVAR+UVBR, 280-700nm). We found a threshold for 305nm and 380nm doses of 1.13 and 9.78 kJ m-2 respectively, below which no UVR effects on stress parameters or toxin production were observed. In addition for 305 nm doses between 1.13 and 1.22 kJ m-2, despite the decrease of Chlorophyll-a, in UVB was evident a significant decrease in reactive oxygen species (ROS, measured by 2′-7′-dichlorodihydrofluorescein diacetate oxidation) due to antioxidant superoxide dismutase (measured by Assay Kit, Cayman Chemical Company) consume [2], as well as a decrease in assimilation number (measured by 14C inoculation) inhibition (%) (ANI). For higher than 1.22 kJ m-2 doses, at 305nm, all stress parameters and ANI, increased significantly, while most of UVR photosynthesis inhibition was due to UVAR. In relation to toxins production, for higher UVR doses, the microcystin (Mcyst, measured as Mcyst-LR equivalents concentrations[1]) were significantly increased in UVB than for UVA and P. These results suggest that UVBR may produce oxidative stress in 4-5h exposure, when the generation of ROS overwhelms the cell's natural antioxidant defenses for highest doses. Acknowledgments: we acknowledges to Dr. S. Díaz who shared the Biospherical Inc. radiometer and Drs. Opezzo - Costa and her group for laboratory support. [1] L. Rosso, D. Sedan, M. Kolman, et al. J Coastal Life Med 2014, 2(4): 287 [2] D. Thomas, T. Avenson, J. Thomas, and S. Herbert. Plant Physiol. 1998, 116: 1593