Functional evolution of giant virus capsids

Introduction

How do viruses identify their hosts in a challenging environment? This question is highly relevant for protist-infecting giant viruses in aquatic ecosystems, where the density of host cells is typically low and random encounters are rare. Giant viruses have genome sizes of up to two megabases and encode a vast genetic diversity, but we know almost nothing about their diverse capsid structures and the various strategies they use for infecting the next host cell.

Background

During the last decade, I have shed light on the symbiotic interactions between marine flagellates, giant viruses, and their virophage parasites. With CAPSOLUTION, I will use our collection of freshwater flagellate cultures to characterize giant viruses with previously unknown capsid structures from oligotrophic lakes.

Recent Discoveries

We recently discovered two giant viruses with unprecedented capsid modifications:

• “Cometa virus”, whose capsid has a bundle of unique head fibers and a conical tail.
• “Sentinel virus”, whose tentacle-like appendages span several micrometers.

Research Objectives

CAPSOLUTION will allow me to characterize the fascinating virion structures of Cometa and Sentinel viruses at molecular resolution and elucidate their function during host attachment and infection.

Key Questions

1. What is the protein composition of these appendages and how are they assembled?
2. How did they evolve?
3. How common and diverse are modified capsids among giant viruses and how do they adapt to environmental constraints?

Methodology

I will address these questions in a multi-disciplinary approach combining:

• The morpho-genomic characterization of natural giant virus communities.
• Structure-function studies of newly isolated virus-host systems.
• Evolutionary analyses of their appendage-associated genes.

Conclusion

CAPSOLUTION will reveal how giant viruses use unique capsid modifications to adapt to their environment, thereby breaking new ground in microbiology and expanding our horizon of virus functioning in freshwater lakes.