STRATEGIES OF ADAPTATION BY ANTARCTIC CYANOBACTERIA TO ULTRAVIOLET-RADIATION

Effects of UVA and UVB radiation were evaluated on two cyanobacterial strains (Phoumidium murrayi and Oscillatoria priestleyi) isolated from the McMurdo Ice Shelf, Antarctica. The two isolates showed some simil arities, but also major differences in their qualitative and quantitat ive responses to ultraviolet radiation (UVR). Growth decreased with in creasing WR, but with a 5-fold (WA) or 10-fold (WE) greater effect on O. priestleyi than P. murrayi. In both isolates, cellular concentratio ns of phycobiliproteins (measured by in vivo absorbance), and to a les ser extent chlorophyll a, diminished with increasing UVR exposure. Spe ctral scans of methanol extracts indicated the presence of UVR-screeni ng compounds in O. priestleyi but not P. murrayi; however, the absorba nce per unit dry weight was low, and similar in cultures with and with out UVR. Carotenoid pigments increased up to a threshold UVB flux and thereafter decreased. In both isolates, moderate WA lessened the effec t of growth inhibition by WE, consistent with a UVA-activated repair m echanism. Comparative motility tests showed that O. priestleyi is a fa st gliding species that can rapidly relocate in response to changes in ambient light, while P. murrayi is non-motile. The ability of O. prie stleyi to escape UVR by gliding, and the greater ability of P. murrayi to tolerate WA and UVB exposure, illustrate the differences in UVR su rvival strategies even between closely related species of cyanobacteri a.