Effects of UV radiation on DNA photodamage and production in bacterioplankton in the coastal Caribbean Sea

This study focuses on the effects of ultraviolet radiation (UVR) on bacteri oplankton. The effect of different parts of the sunlight spectrum on the le ucine and thymidine incorporation and on the induction of DNA damage in nat ural bacterial populations in the coastal Caribbean Sea off Curacao were in vestigated. DNA photodamage in microorganisms and biodosimeters was quantif ied by the number of cyclobutane dimers (thymine dimers). Increasing DNA da mage during the day was found when incubated in full surface solar radiatio n. When UVBR was excluded no DNA damage was observed, indicating that thymi ne dimers were only formed by WE radiation. The amount of thymine dimers in the >0.8 mu m fraction was only one-third of the amount of induced thymine dimers in the <0.8 mu m fraction, suggesting that phytoplankton is less se nsitive to UV-induced DNA damage than bacterioplankton. Protein and DNA syn thesis was inhibited to about 30% of the dark control during the day when e xposed to surface solar radiation. In both protein and DNA synthesis a tren d was found, with the highest inhibition under full solar radiation. lower inhibition when UVBR was shielded off and the lowest inhibition when UVAR ( <375 nm) was also shielded off. The intracellular carbohydrate content of t he phytoplankton incubated under full solar radiation was not significantly higher than the dark incubation, while the contents after incubation witho ut UVBR were significantly higher. The carbohydrate content in the samples incubated without UVBR and UVAR (<375 nm) was a little higher than with onl y UVBR shielded off. In summary, the results show that in the coastal Carib bean Sea UVBR is responsible for DNA damage in bacterio- and phytoplankton, while protein and DNA synthesis in bacterioplankton was inhibited by UVBR, WAR and PAR and carbohydrate synthesis in phytoplankton by both UVBR and U VAR.