PHYVIR

Phytoplankton (tiny ocean plants) produce half the Earth’s oxygen and feed the seas but are infected by viruses. Although we have all experienced the massive effect viruses can have at local and global scales, very little is still known about their impact on phytoplankton in the oceans. The PHYVIR research project aims to fill this knowledge gap, by investigating virus-phytoplankton interactions in the laboratory and during oceanic expeditions, and by building advanced computer models to predict how marine viruses affect carbon and nutrient cycling in the ocean and, thus, our planet's health.

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Why viruses matter for the ocean

Marine phytoplankton are responsible for about 50% of global oxygen production and sequester vast amounts of anthropogenic CO2. Viral infection kills host cells (viral lysis) and so redirects the flow of energy and elements through the ecosystem, with far-reaching consequences for ocean structure and functioning.

Several things are still poorly known:

  • How fast viruses kill different phytoplankton groups (lysis rates).
  • How infection changes the elemental composition (stoichiometry) and traits of the host.
  • How environmental stressors linked to climate change alter virus–host interactions.
  • How virus and host traits are distributed geographically.

Global ecosystem and biogeochemical models usually leave virus–host dynamics out, include them only implicitly, or treat all phytoplankton groups alike.

Five linked objectives

  1. Single host–virus systems. Detailed trait characterisation, elemental stoichiometry and gene expression for the major phytoplankton groups, used to evaluate a mechanistic trait-based model.
  2. Multi-host laboratory systems. How viral infection affects competition, particularly under nutrient limitation and temperature shifts.
  3. Semi-natural communities. Manipulated communities to study effects on host gene expression and trait distribution under the same stressors.
  4. Atlantic fieldwork. Phytoplankton and virus biogeography from the tropics to sub-polar waters, with population-specific viral lysis rates and the active infections identified by cell sorting and targeted omics.
  5. Global models. Phytoplankton–virus interactions integrated into global marine ecosystem models, validated against large-scale patterns of lysis rates and viral biogeography.