Weinbauer, M.G., S.W. Wilhelm, D.R. Garza and C.A. Suttle. 1996. Photorepair restores UV-radiation-induced damage in marine bacteriophages and maintains high bacterial mortality. Eos 76(3 suppl):OS208.

Photoreactivation is the process whereby DNA damaged by UV-B radiation (280 - 320 nm) is repaired by the light activated (350 - 500 nm) enzyme, photolyase. While photoreactivation is relatively well understood, its role in the repair of DNA in nature is largely unknown. The potential significance of photoreactivation for phage communities was examined for viruses concentrated from samples collected in the Gulf of Mexico. Samples were collected between 1000 h and 1800 h from several depths corresponding to a range of UV-B radiation between 1 and 100 % of the surface. In 66.7 % of the samples the infectivity of naturally occurring viruses was restored by the photoreactivation system of Vibrio natriegens. The infectivity of these viruses could not be restored by light-independant repair mechanisms. To assess the significance of photoreactivation for whole natural virus communities, viruses in the <0.2-µm fraction of seawater were exposed to sunlight, in order to damage viral DNA. Viruses with damaged DNA were added back to the natural bacterial community and exposed to photoreactivating wavelengths of sunlight, or kept in the dark. Between 15 and 53 % of the total natural virus community could be photoreactivated, but not dark repaired. These results indicate that photoreactivation can compensate for a major fraction of UV radiation induced damage and thus may be vital for the survival of viruses in surface waters. This also implies that a high viral mortality of bacteria is maintained, since every virus which is repaired by a host ultimately lysis the cell and thus contributes to the mortality of bacteria.

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