Estimating viral impact and Cost of Resistance on marine phytoplankton communities

Numbering in excess of 10 million per teaspoon of seawater viruses are interacting with their cellular counterparts in the microbial kingdom on an unforeseen scale. Notably, viral lubrication of the ocean's microbial machinery has enormous implications for global biogeochemical cycling and ecosystem function. VIMPACT, standing for "Viral Impact", departed from a conceptualized planktonic food web to empirically test key parameters regulating the interactions between marine viruses and their phytoplanktonic hosts. Vimpact?s ultimate goal was to assess the real impact viruses might have on phytoplankton and microbial marine communities, and contribute to the development of improved planktonic food web models with enhanced validity as tools for marine ecosystem management. Vimpact?s overall results confronted the initial hypothesis that viruses play a fundamental role in the maintenance of high microbial diversity in marine environments. While that impact could sometimes be perceived, we did not observe a clear and consistent link between high microbial diversity and viral concentration, not did we observe clear phytoplankton fitness trade-offs associated with resistance to viral infection. Vimpact made important contributions to our knowledge of the patterns that emerge form host-virus interactions in the marine environment. New protocols were optimized which confer technical achievements to be further used in a better exploration of those patterns in the future. We confirmed existing hypothesis and added empirically derived values for microbial and viral life-trait parameters that can be used in modelling efforts. Above all this project unveiled significant challenges to currently existing assumptions, which will undoubtedly be considered if we are to build more accurate models of phytoplankton-virus dynamics in the oceans.

Numbering in excess of 10 million per ml of seawater it is now well acknowledged that viruses are interacting with their cellular counterparts in the microbial kingdom on an unforeseen scale. Notably, viral lubrication of the ocean's microbial machinery i s a critical regulator of vertical carbon transport in marine food webs. Although still poorly understood, we now know that the way viruses interact with and shape marine microbial communities has enormous implications for global biogeochemical cycling an d ecosystem function. Two decades of continuous efforts in our group to conceptualize this viral impact have led to the Killing the Winner (KtW) model, recognized as the most accurate representation of cell-virus interactions in the planktonic realm. Part icularly, by differentiating viral impact on microbial hosts with different growth and immunity capacities, KtW explains the fundamental importance of viruses for the existence of highly dynamic and diverse microbial communities. This model can be an impo rtant tool for our understanding and management of marine ecosystems. In that sense, it is indispensable an empirical derivation of its variables and evaluation of its predictions. With VIMPACT we will: 1) confront the theoretical assumptions of KtW with empirically derived values for its key parameters, 2) evaluate KtW predictions at increasing complexity levels, from strain to natural phytoplankton communities, and 3) reassess and improve the currently existing model in light of the empirically-driven r esults. In order to achieve these goals, and in collaboration with an international team of recognized specialists in marine microbiology, we will make use of the latest technology available in microbiology and metagenomics to keep Norwegian research on t he fore front of this very promising field.