Characterization of Dissolved DNA in the North Pacific Subtropical Gyre

Dissolved DNA (D-DNA) is operationally defined as DNA that passes through a 0.1 micrometer filter. It is ubiquitous in nature yet its sources, sinks and ecological characteristics are largely unknown. One reason for the uncertainty is the methodological limitation that precludes a distinction between viral DNA and exocellular free DNA (F-DNA) which are the two pools that comprise dissolved DNA. We describe a method that provides complete separation of the dissolved DNA components with subsequent downstream analysis and quantification. This method was applied to water column samples collected from the oligotrophic North Pacific Subtropical Gyre to provide a fully sequenced dataset of open-ocean free DNA. We quantify and characterize concentrations of total dissolved DNA, viral DNA, and F-DNA. These results highlight the composition of F-DNA in different regions of the water-column (euphotic and mesopelagic) and describe the implications for dissolved organic matter cycling and export as a delivery mechanism. As a common component of dissolved organic carbon, it is predicted that F-DNA plays an important role in the cycling of labile organic matter and may facilitate the transfer genetic information between marine microorganisms.