Uncovering key players for regulation of phytoplankton function and structure: lessons to be learned from algal virus-haptophyte coexistence

As described earlier, we have conducted extensive infection experiments (both acute and persistent systems) where we detail the infection patterns (different characteristics) of the various virus-host systems as previously described. The manuscript describing these progressions is almost complete and will be submitted to an internationally renowned journal shortly. During the infection experiments described earlier, samples were taken for transcriptomic analyses, providing insights into the gene regulation patterns of the various systems, both during the infection process itself and in the development of resistance mechanisms. We have completed analyses of the virus's progression in infection but have chosen to wait for the host's response until all host genomes are fully annotated (see point 5). As described earlier, the time it takes for the virus to lose its ability to infect the host cell when exposed to various environmental factors is an important characteristic. As previously described, we have conducted measurements in the ocean to determine the time it takes for viruses to break down and lose the ability to infect new host cells. Additionally, we have created simulations to see if we can find an explanation for whether different processes govern the breakdown of virus particles and the loss of inefficiency. We have completed the analysis of these data and are in the process of finalizing the work. By using new high-resolution microscopy techniques combined with proteomics, we have examined differences in structure and infection progress of the various virus systems. This work is a collaboration with Carmen San Martin (Centro Nacional de Biotecnología Madrid, Spain). A postdoc at VirVar has worked (guest grant - VirVar) at this institute to solve the structure of the most complex virus (PkV RF01) in our collection. The work is nearing completion, and we have discovered structures that are unlike any other structures in described viruses. Based on these results, we are now able to present a hypothesis on how this virus can infect its host cell using an inner cylindrical structure that is ejected and transports the virus's DNA into the host cell. A PhD student at CNB-CSIC is continuing to work on solving the structure of PkV RF02. This is part of her PhD work. Through the JGI project (Joint Genome Institute project no. DS 505156), as mentioned earlier, we have completed the sequencing of Haptolina ericina, which is the host for two of our viruses. Annotation (prediction of the function of individual genes) of this genome has also been completed in collaboration with UiO. The other two algae (two strains of Prymnesium kappa) have been sequenced, and we will continue to work on annotating these genomes with UiO. Description of the genomes of PkV RF02 and HeVRF02 has shown that these two viruses have played an important role in the evolution of proteins involved in DNA packaging in the cell nucleus of a distantly related algal group, namely Dinoflagellates. Analyses of these two virus genomes are complete, and we are well underway in writing this manuscript.

VirVar seeks to discover basic mechanisms of virus-host interaction that contribute to a general understanding of how viruses affect the biodiversity of their host population in the marine microbial foodweb. The microbial food web is the link between ocean biogeochemistry and the marine food-web, thus knowledge about how processes are regulated in the microbial part of the food-web is essential for the understanding of how energy and matter is transferred to higher trophic levels. VirVar will focus on unique viral-host isolate pairs as model systems using keystone phytoplankton hosts (haptophytes) of great importance for world’s oceans, including Arctic oceans. We will gain fundamental knowledge by using virus-host model systems that are at different evolutionary stages (recent/acute to established/persistent) to gain a basic understanding of success factors (fitness traits-trade-offs) and their effect on variation and change in the structure and function of marine phytoplankton communities. Our model systems will allow us to elucidate evolutionary and ecologically important factors that have resulted in different strategies for a successful co-existence from strain to natural community level. This information is crucial in the understanding of viral ecology in a changing ocean, including the Arctic environment.