Sunlight-induced DNA damage in marine micro-organisms collected along a latitudinal gradient from 70 degrees N to 68...

We examined ultraviolet radiation (UVR)-induced DNA damage in marine micro-organisms collected from surface seawater along a latitudinal transect in the Central Pacific Ocean from 70 degrees N to 68 degrees S. Samples were collected predawn and incubated under ambient UVR in transparent incubators at in situ temperatures until late afternoon at which time they were filtered into primarily bacterioplankton and eukaryotic fractions. Cyclobutane pyrimidine dimers (CPDs) and (6-4) photoproducts [(6-4)PDs] were quantified in DNA extracts using radioimmunoassays. UVB was lowest in the polar regions and highest near the equator and correlations between UVB and DNA damage were observed. The eukaryotic fraction showed significant CPDs across the entire transect; (6-4)PDs were detected only in the tropics. The bacterial fraction showed no accumulation of (6-4)PDs at any latitude, although residual (6-4)PDs were observed. Bacterial cell volumes were greatest in the sub-Arctic and northern temperate latitudes and lower in the tropics and southern hemisphere, a unique observation that parallels Bergmann's rule. A strong negative correlation was observed between cell volume and CPDs. The environmental impact of solar UVR on marine micro-organisms in the open ocean is complex and our results suggest that several factors such as DNA repair, cell size, temperature, salinity, nutrients and species composition are important in determining relative sensitivity.