THE ROLE OF SUNLIGHT IN THE REMOVAL AND REPAIR OF VIRUSES IN THE SEA

We investigated the in situ destruction rates of marine viral particle s as well as the decay rates of infectivity for viral isolates along a n similar to 400-km transect from oligotrophic offshore waters to prod uctive coastal waters in the Gulf of Mexico. Light-mediated decay rate s of viral infectivity averaged over the solar day ranged from 0.7 to 0.85 h(-1) in surface waters at all stations and decreased with depth in proportion to the attenuation of UVB (305 nm). The destruction rate s of viral particles also decreased with depth, although the rates of particle destruction were only 22-61% of infectivity when integrated o ver the mixed layer. The rates of viral particle destruction indicated that at three of four stations 6-12% of the daily bacterial productio n would have to be lysed in order to maintain-ambient viral concentrat ions. At the fourth station, where there was a dense bloom of Synechoc occus spp. and the mixed layer was shallower, 34-52% of the daily bact erial production would have to be lysed. A comparison of the differenc e between destruction rates of viral particles and infectivity integra ted over the depth of the mixed layer implies that host-mediated repai r must have restored infectivity to 39-78% of the sunlight-damaged vir uses daily. The calculated frequency of contacts between viral particl es and bacterial cells that resulted in infection (contact success) ra nged from similar to 18 to 34% in offshore waters, where the frequency of contacts between viruses and bacteria was much lower, to similar t o 1.0% at the most inshore station, where contact rates are much highe r. This suggests that in offshore waters bacterial communities are les s diverse, and that there is less selection to be resistant to viral i nfection. This paper provides a framework for balancing viral producti on, destruction, and Light-dependent repair in aquatic viral communiti es.