An article published in the journal “eLife” describes a research on a species of giant virus called Bodo saltans virus (BsV), considered part of the most abundant group present in the seas. The name is due to the fact that it infects a species of microscopic plankton called the Bodo saltans. A team of researchers from the University of British Columbia succeeded in isolating this virus, classified as a Klosneuvirus, a sub-group of the Mimiviridae family.
The DNA of Bodo saltans virus has about 1.39 million bases and this makes it one of the largest viruses isolated so far and the largest among the ones that infect zooplankton. This research brought a significant step forward in the investigation of the giant viruses present in the sea, since so far there was no way to conduct them in lab. Viruses belonging to the Klosneuvirus group were also discovered in the data collected by the Tara Oceans expedition.
Klosneuviruses were discovered in 2017 and are the most recent group of giant virus discovered since 2003. There are discussions about their origins and their evolution and each new species discovered and studied offers new information on these viruses that can have a size larger than some bacteria.
The examination of Bodo saltans virus showed that its DNA, huge for a virus, allows it to generate toxins and enzymes that probably interfere with the attacks of other viruses. It also generates proteins from a group that’s probably used to fight its hosts’ antiviral systems. In essence, it tries to monopolize its hosts’ exploitation and at the same time could be engaged in a sort of evolutionary arms race with its hosts.
The image (courtesy Christoph Deeg, Curtis Suttle, University of British Columbia, All Rights Reserved) shows on the left a cell of Bodo saltans 24 hours after being infected by the virus and on the right the situation after the virus has matured. The virus is indicated by the arrows.
The DNA of the Bodi saltans virus shows a remarkable gene duplication and the possibility to modifly quickly, adapting to environmental changes. The analysis of these characteristics will help to understand the origin of this virus and other giant viruses. The hypotheses are that they descend from bacteria that lost the ability to reproduce on their own and became parasites and that they descend from normal-size viruses that acquired a huge amount of genes from other organisms during their evolution.