AMBIENT SOLAR RADIATION-INDUCED PHOTODAMAGE IN MARINE BACTERIOPLANKTON

There has been much recent concern about the effects of increased UV r adiation at certain locations on the earth's surface. There have been extensive studies of ultraviolet radiation effects on phytoplankton an d primary production, yet the effects of UVB upon bacterioplankton hav e been largely overlooked, Bacteria play a central role in the cycling of nutrients and energy flow to higher trophic levels, serving as bot h mineralizers and secondary producers that are consumed by higher org anisms, We have begun to investigate the induction of DNA photodamage by UVB in marine planktonic communities using a highly specific radioi mmunoassay to measure cyclobutane pyrimidine diners in samples collect ed from the northern Gulf of Mexico. DNA damage in the bacterioplankto n size-fraction (<0.8 mu m) was greater than in the larger eukaryotic size fraction (>0.8 mu m <120 mu m) in 9 of 10 samples, Diel patterns of dimer accumulation and repair were observed in surface waters over a 48 h period in the bacterioplankton size fraction and in the larger eukaryotic plankton size fraction, Depth profiles of DNA damage in the bacterioplankton size fraction appear to be dependent on surface wate r mixing, Damage was greatest in surface waters, decreased with depth and could be detected to 10 m in calm seas, No net accumulation of dam age was observed in moderate seas, even at the surface, Solar radiatio n was found to inhibit significantly both H-3-thymidine and C-14-leuci ne incorporation. Ultraviolet B was responsible for approximately bah of the total inhibition of H-3-thymidine incorporation, UVA contributi ng the other half of the inhibition, The vast majority of C-14-leucine incorporation inhibition was due to UVB, suggesting that protein synt hesis is less affected by UVA. The results demonstrate that direct mea sures of DNA damage can be made of indigenous planktonic communities a nd that bacterioplankton are highly susceptible to UVB damage and may serve as a more sensitive indicator of UVR stress than other microorga nisms.