photoreactivation compensates for UV damage and restores infectivity to natural marine virus communities

We investigated the potential for photoreactivation to restore infectivity to sunlight-damaged natural viral communities in offshore (chlorophyll a, <0.1 mg liter21), coastal (chlorophyll a, ca. 0.2 mg liter21), and estuarine (chlorophyll a, ca. 1 to 5 mg liter21) waters of the Gulf of Mexico. In 67 % of samples, the light-dependent repair mechanisms of the bacterium Vibrio natriegens restored infectivity to natural viral commu-nities which could not be repaired by light-independent mechanisms. Similarly, exposure of sunlight-damaged natural viral communities to>312-nm-wavelength sunlight in the presence of the natural bacterial commu-nities restored infectivity to 21 to 26 % of sunlight-damaged viruses in oceanic waters and 41 to 52 % of the damaged viruses in coastal and estuarine waters. Wavelengths between 370 and 550 nm were responsible for restoring infectivity to the damaged viruses. These results indicate that light-dependent repair, probably photoreactivation, compensated for a large fraction of sunlight-induced DNA damage in natural viral com-munities and is potentially essential for the maintenance of high concentrations of viruses in surface waters. The UV-B radiation (280 to 320 nm) that reaches the Earth’s surface can penetrate to considerable depth in seawa-ter (27) and cause significant damage to a variety of marin