Several kilometers below the surface, Pacific sediments harbor a viral diversity whose vast majority had still escaped scientific databases.
Researchers focused on the Clarion-Clipperton Fracture Zone in the central Pacific. This immense region contains numerous metal-rich nodules, particularly manganese, nickel and cobalt. It is therefore also attracting attention for future deep-sea mining projects.
Seafloor in the Clarion-Clipperton Zone covered with manganese nodules, photographed by the KIEL 6000 ROV during the SO239 expedition in 2015.
Credit: KIEL 6000 ROV, GEOMAR, CC BY 4.0.
Image Wikimedia
Sediment cores collected from the seafloor made it possible to analyze the genetic material present in this environment. The researchers thus compiled a catalog of 11,742 distinct viral genetic sets. This approach makes it possible to detect viruses without having to cultivate them in the laboratory, which would often be impossible.
The result primarily reveals the extent of what remained unknown. More than 99% of the viral groups identified were not represented in any of the major reference databases used for comparison.
These viruses are not presented as a threat to humans. The analyses indicate that they primarily infect bacteria and archaea, two major groups of single-celled microorganisms. These organisms directly participate in the cycling of carbon, nitrogen, phosphorus, sulfur and metals in the sediments.
In practical terms, a virus can alter the functioning of the cell it infects. Some of the genomes identified carry genes capable of affecting their host’s metabolism during infection.
The analyses show gene exchanges that could help certain microbes better withstand a metal-rich environment. Viruses could therefore contribute indirectly to their local adaptation. Their role extends beyond the mere destruction of cells and also affects the overall functioning of this deep ecosystem.
This discovery comes in a region where the extraction of metal nodules remains highly debated. The study does not measure the consequences of mining and cannot directly predict its effects. It does, however, provide a baseline before any potential large-scale disturbances.
Researchers will now be able to compare this catalog with future samples collected from intact or disturbed areas. This comparison will show which viral groups disappear, emerge or change in abundance when seafloor sediments are altered.