Assessing multi-dimensional physical fractionation of phytoplankton as a means to identify uncultivated virus-host systems

Abstract

Novel marine viruses are regularly being identified using molecular techniques. However, the role of these viruses in marine ecology, and by extension biogeochemical processes in the ocean, is not fully understood. To fully appreciate their role in marine processes it would be helpful to identify the host species that these viruses infect. Although culturing has been utilized to successfully identify virus host systems, most of the new viruses identified by molecular methods have yet to be cultivated. One possible approach to identifying virus-host pairs without cultivation would be to physically separate populations of cells and identify the viruses specifically associated with a given cell population. For this approach to work, populations of cells must be cleanly separated from one another and from any free viruses. For my thesis project, I evaluated the effectiveness of various methods of physically fractionating plankton communities, both individually and in series, and tested whether specific viruses could be detected in association with the individual cell fractions. The results of the three trials suggest that bulk physical separation of planktonic cells can be used to partially purify individual populations of cells, and that viruses can be detected in association with those cells. Further refinement of the fractionation procedures to achieve pure cell populations may ultimately allow for definitive linkages between uncultivated plankton and the viruses that infect them. The plankton fractionation procedures tested in this study may also prove useful for other types of population-specific analyses of uncultivated plankton.