AME 20:49-58 (1999)  -  doi:10.3354/ame020049

ABSTRACT: This study focuses on the effects of ultraviolet radiation (UVR) on bacterioplankton. The effect of different parts of the sunlight spectrum on the leucine and thymidine incorporation and on the induction of DNA damage in natural bacterial populations in the coastal Caribbean Sea off Curaçao were investigated. DNA photodamage in microorganisms and biodosimeters was quantified by the number of cyclobutane dimers (thymine dimers). Increasing DNA damage during the day was found when incubated in full surface solar radiation. When UVBR was excluded no DNA damage was observed, indicating that thymine dimers were only formed by UVB radiation. The amount of thymine dimers in the >0.8 μm fraction was only one-third of the amount of induced thymine dimers in the <0.8 μm fraction, suggesting that phytoplankton is less sensitive to UV-induced DNA damage than bacterioplankton. Protein and DNA synthesis was inhibited to about 30% of the dark control during the day when exposed to surface solar radiation. In both protein and DNA synthesis a trend 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 the phytoplankton incubated under full solar radiation was not significantly higher than the dark incubation, while the contents after incubation without UVBR were significantly higher. The carbohydrate content in the samples incubated without UVBR and UVAR (<375 nm) was a little higher than with only UVBR shielded off. In summary, the results show that in the coastal Caribbean Sea UVBR is responsible for DNA damage in bacterio- and phytoplankton, while protein and DNA synthesis in bacterioplankton was inhibited by UVBR, UVAR and PAR and carbohydrate synthesis in phytoplankton by both UVBR and UVAR.

KEY WORDS: UV radiation · Bacterioplankton · DNA damage · Bacterial production · Phytoplankton · Carbohydrates