Project: Collaborative Research: Constraining virus loss and carbon and nitrogen flow through virovory in temperate marine ecosystems with isotope tracing and microbial food web models.

Overview: 

A quantitative understanding of the flow of nutrients and energy in marine ecosystems is critical to understand the availability and dynamics of the resources that support the marine food web and the capacity of the ocean to store carbon under changing climate conditions. Virus particles and infections play a role in the biological cycling and sequestration of organic matter by increasing the flow of organic matter to the dissolved phase fueling the microbial loop—‘viral shunt’ and releasing compounds during host cell lysis that enhance the formation of particle aggregates and the sinking of organic matter through the biological pump—‘viral shuttle’. Quantification of virus decay and removal is critical to constrain infection dynamics in models, which is a first step to quantify the ‘shunt’ and ‘shuttle’. Direct consumption of virions by protists - virovory - is a potentially dominant virus loss process, a source of nutrition to grazers, and a significant food web pathway that redirects nutrients and energy to upper trophic levels. However, the magnitude of each of these virally-mediated processes of regeneration, sequestration, and trophic transfer remains largely unresolved. Here, we propose laboratory incubations of isotope labeled viral particles in either microbe-free seawater or seawater that includes bacteria and/or protists collected from an oceanic oligotrophic site and a eutrophic coastal site at different times of the year to test the following hypotheses: 

H1. Virovory is a natural sink of marine viruses that rivals all other viral losses combined. 

H2. Nutrient transfer from large enveloped dsDNA eukaryotic viruses is higher than from smaller virus particles. 

H3. Virovory contributes more nutrition for heterotrophic protists in permanently or seasonally oligotrophic waters that in eutrophic marine ecosystems. 

We will use the empirical data to parameterize virovory in ecosystem models. 

Intellectual Merit:

The premise of this proposal is that viruses play multiple and dynamic roles in the fate of organic matter and the flow of energy in the ocean. Arguably, the least studied of those roles is the direct transfer of nutrients and energy up the food web through grazing on virus particles - virovory. This study’s driving concept is that virovory’s impact on the cycling of organic matter and the contribution to grazers’ nutrition varies spatiotemporally across taxa of heterotrophic bacteria and protists (including mixotrophs), yet on a local and global scale, virovory could rival viral loss rates due to other biotic and abiotic factors. Although the idea that viruses are a valuable food source for aquatic organisms is not novel, it is only now starting to gain attention as a potentially sizeable mechanism for carbon flux. Consequently, results from this project could transform our understanding of the true impacts of viruses in the marine environment beyond their role as predators. Furthermore, the proposed work is timely and complementary to large-scale projects, including work supported by the NSF and NASA, to create a predictive understanding of the ocean’s carbon cycle. Notably, such studies largely ignore the viruses. 

Broader Merits:

The quantitative and mechanistic understanding of the impact of virovory on nutrients and energy fluxes gained through this study will interest scientists in subdisciplines across biological oceanography, chemical oceanography, and microbial ecology and biology. Funding from this award will directly support the training of one postdoctoral researcher, one graduate student, and several undergraduate students at and across both collaborative institutions. The training will include new scientific skills and other important professional development needs for careers inside and outside academia, e.g., teaching and mentoring experience, science communication to diverse audiences, proposal preparation, and reporting. Significant efforts will be made to recruit individuals from underserved and underrepresented communities in STEM. The PIs and other team members will also disseminate scientific advancements made through the project by participation in educational activities for middle to high school students and public discussions at their institutions. The success of these activities will be evaluated through mechanisms and metrics established at the PIs institutions that consider scientific outcomes, career progression, and retention of the participants in STEM fields.