Wilhelm, S.W., M.G. Weinbauer, D.R. Garza, R. Pledger, D.L. Mitchell, and C.A. Suttle (submitted). Sunlight-induced DNA damage and in marine viral communities. Abstracts of the American Society of Limnology and Oceanography, Santa Fe, NM, February 1997.

To develop a better understanding of viral dynamics in marine systems, we have been investigating the impact of solar radiation on viral communities. Radio-immuno assays were used to quantify the solar-radiation induced formation of cyclobutane pyrimidine dimers (CPDs) and pyrimidine (6-4) pyrimidone photoproducts in viral DNA along transects in the Gulf of Mexico. CPD concentrations were consistently ten fold higher than (6-4) photo-product concentrations. The accumulation of photodamage and effect of sunlight on infectivity was greater in the bacteriophage PWH3a-P1 than in the cyanophage S-PWM3, which were deployed in situ for the entire solar day. Moreover, photodamage in the isolates was significantly higher offshore than at the coast. In natural viral communities collected from surface waters we found an accumulation of photodamage during the solar day, with a removal of photodamage at night. Integration of photodamage over depth showed similar values for the offshore stations and one shallowly mixed coastal station, whereas at the other coastal stations there was no detectable accumulation. Results demonstrate that the rate and depth of mixing combined with light-penetration and host-mediated DNA repair play critical roles in maintaining the high abundance of infectious viruses in surface waters.