Viruses as regulators of nutrient cycles in aquatic environments

Viruses are abundant and dynamic members of marine environments. The persistence of viral communities in aquatic systems requires the daily destruction of a significant proportion of the bacterial and phytoplankton populations. While the destruction of host cells by viruses has several implications, one of the most important effects may be the role viruses play as regulators of nutrient cycles. Over the last several years we have obtained estimates of viral turnover rates and viral production for a variety of environments. We have used these estimates to infer the remobilization of nutrients in marine systems attributable to viral lysis. For example, viral lysis of bacterioplankton in the western Gulf of Mexico was estimated to liberate 0.12 to 0.55 μg C L d in offshore waters and 0.72 to 5.2 μg C L d in coastal waters. Similarly, virally mediated carbon release in the Strait of Georgia, British Columbia, ranged from 1.0 to 8.3 μg C L d, with the highest estimates associated with strong tidal mixing. Viruses also play an important role in the remobilization of organic nutrients and trace elements. For example, in the Strait of Georgia viral lysis was estimated to result in the remobilization of 0.3 to 1.7 ug L d of organic nitrogen, 0.03 to 0.14 ug L d of organic phosphorus and 0.06 to 0.33 ng L d of organically complexed iron. The information presented demonstrates the importance of including viral processes in models of marine carbon and nutrient fluxes.