The Oceans not only host large predators such as sharks or orcas. Even in the realm of the microscopic some unicellular species consume others. Choanoflagellates belong to these unicellular predators. They are widespread in the ocean and eat bacteria and small algae. Choanoflagellates are considered among the closest living unicellular relatives of animals and can transition to a multicellular state. For that reason they are often studied for understanding how multicellular organisms like us came to be.

Now, a team of scientists led by Professor Alexandra Z. Worden (GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany/Monterey Bay Aquarium Research Institute, MBARI, USA) has provided the first insights in the interaction between choanoflagellates and viruses. In a multi-year intensive effort the team was able to detect the genome of a giant virus in these unicellular predators. The virus had a genome size and gene numbers comparable to small bacteria. More surprising than the genome size were the many functions it encodes and brings to the host. The study has just been published in the international journal Proceedings of the National Academy of Sciences USA.

For the study the scientists repeatedly went to sea with high-tech instrumentation and the goal to look at all the predatory unicellular organisms in the water using a laser-based visualization system. Then they individually separated these cells from other microbes in a process called single-cell sorting. “Each individual predator from the wild was then sequenced – and the single-cell sorts from one Pacific Ocean sample were dominated by an uncultured species of choanoflagellate”, Professor Worden explains.

Read more at: Helmholtz Centre for Ocean Research Kiel (Geomar)