Scientists Uncover Hundreds of Mysterious Giant Viruses in Ocean Depths

Giant Viruses Discovered in Ocean Depths: What We Know

Scientists at the University of Miami have uncovered 230 previously unknown “giant viruses” (giruses) lurking in oceans worldwide. Rivaling bacteria in size, these viruses are five times larger than typical viruses and could impact ecosystems in ways still being understood.

Size and Scope

Most viruses measure 20–200 nanometers, but giant viruses exceed 1,000 nanometers—visible under microscopes, though still far smaller than a human hair (80,000–100,000 nanometers). These viruses primarily infect algae and amoebas but may also thrive on land. While not yet linked to human harm, their ecological role is critical.

Giant viruses burst from algae cells, releasing their genetic material (Credit: University of Miami).

Ecological Impact

Giant viruses target algae, which produce half of Earth’s oxygen. By collapsing algal blooms—vast oceanic algae colonies—they risk disrupting oxygen levels and marine ecosystems. Rapid bloom die-offs can deplete atmospheric oxygen, though excessive blooms (sometimes toxic) also pose threats.

Pandoravirus salinus, discovered in Chilean sediments (Credit: Nature npj Viruses).

Hidden Diversity

Using software BEREN, researchers analyzed seawater DNA to identify virus genomes. Most giant viruses fell into two groups:

• Algavirales (135 types): Infect algae, aiding carbon cycling.
• Imitervirales (81 types): Genetically flexible, potentially broader hosts.

Their large genomes (up to 100x more genes than average viruses) let them manipulate host metabolism during infection. “They may reshape marine biochemistry,” said lead author Benjamin Minch.

Distribution of giant virus types found in the study (Credit: University of Miami).

Where They Thrive

Most giant viruses were found in colder waters:

• Baltic Sea: 108 types
• Antarctic: 65 types
  Others appeared in the Arctic, South Pacific, and Korea’s Jangmok Bay. Their cold adaptability raises concerns about climate change impacts.

Baltic Sea: A hotspot for giant viruses (Credit: University of Miami).

The Biggest Virus Known

Pithovirus, the largest at 1,500 nanometers, was found in 30,000-year-old Siberian permafrost. It remains infectious, highlighting the resilience of giant viruses.

Future Research

Published in Nature npj Viruses, the study underscores the need to explore terrestrial giant viruses and their roles in ecosystems. “Our framework improves pollution and pathogen monitoring,” Minch noted, emphasizing the urgency as climate change threatens cold-water virus habitats.

Structure of a giant virus (Credit: Nature npj Viruses).

These discoveries reveal a hidden layer of oceanic life, balancing ecosystems in ways science is just beginning to unravel.