What if the cold soils of Scandinavia hid still unsuspected life forms? For the first time in Finland, scientists have just uncovered a giant virus, called Jyvaskylavirus, which could well change our understanding of these fascinating entities, long considered as simple parasites.
200 nanometers in diameter
The team of the Nanoscience Center of the University of Jyväskylä isolated this virus from environmental samples, as part of a study recently published in the journal eLife. By exposing amoeba crops (Acanthamoeba Castellanii) to soil samples, researchers observed the appearance of a particular infection agent: a viral particle of 200 nanometers in diameter, twice the size of a flu virus, and almost as large as a bacteria.
If giant viruses were discovered for the first time in the early 2000s, their diversity remains largely unexplored. The Jyvaskylavirus therefore joins this strange family whose members – often more complex and larger than the viral norm – shake up the classic definitions of the living.
A Finnish cousin from Marseillevirus
By analyzing its structure and genome, scientists discovered that this virus was genetically related to Marseillevirusa line of giant viruses isolated for the first time in an air conditioning tower in Marseille in 2009. These viruses belong to a group called Marseilleviridae, which mainly infect amoebas and have a genome of around 350,000 pairs of bases, much larger than that of conventional viruses.
The Jyvaskylavirus Sharing with its southern cousins a set of characteristic genes linked to replication, repair of DNA and still mysterious functions. These similarities have been highlighted thanks to a complete genomic sequencing, followed by comparative analyzes carried out with international databases bringing together other known giant viruses.
This unexpected genetic kinship between a virus in northern Europe and a southern virus reveals surprising scalable trajectories, perhaps due to still misunderstood dispersion mechanisms. These viruses may have traveled with their microscopic hosts through the floor, water or even via migratory birds. Another hypothesis: they could share an older common ancestor than we thought, which would question certain models of viral evolution.
Beyond genetics, morphological similarities have also been noted: the Jyvaskylavirus has a typical Icosaedrical capsid (protein envelope) Marseillevirusand the Images in helium ion microscopy have shown a very similar fixing mode on amoeba cells.
A much more widespread presence than we thought
So far, giant viruses had been mainly detected in Western Europe and South America. Their presence in Nordic soils shows that they are much more widespread than we thought. “” This discovery suggests that giant viruses play an important ecological role even in cold environments “, Underlines Professor Lotta-Riina Sundberg, manager of the study.
And their function could be crucial: regulation of microbial populations, influence on the cycles of nutrients, even complex interactions with other microorganisms. These invisible actors could however play a major role in the ecological balance of soils and aquatic environments.
A biology still full of mysteries
In addition to their impressive size, giant viruses intrigue by their biological complexity: some have hundreds of genes, some capable of code for functions that were not expected to find in viruses, such as DNA repair mechanisms or metabolic tools.
The discovery of jyvaskylavirus therefore opens the way to new questions on viral evolution, on the way in which these entities interact with their hosts-especially amoebes-and on their origin still debated: are they vestiges of old cell life forms, or particularly advanced viruses?
A hunt for giants who just starts
This virus may only be the emerged part of a biological iceberg still poorly explored. Finnish scientists have also detected other giant viruses in their samples, still under study. What is certain is that cold environments, long neglected, are now considered promising reservoirs of viral biodiversity.
While our gaze on viruses continues to expand, the jyvaskylavirus reminds us that the microscopic world is far from having delivered all its secrets – and that even under our feet, in a handful of earth, can hide from the giants.
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