London Daily

Focus on the big picture.
Thursday, Jul 10, 2025

We Know Almost Nothing About Giant Viruses

We Know Almost Nothing About Giant Viruses

An enigmatic group of microbes seems to have an unusual new ability.
In garden ponds and in oceans, in desert soil and in industrial water-cooling towers, matters of life and death are playing out unseen by the human eye. Here, giant viruses prey on single-celled hosts such as amoebas or algae. This microscopic bloodbath can happen on such a large scale that massive algae blooms visible on the ocean surface turn white, as dead algae fade to reveal their colorless skeletons.

Giant viruses, a group discovered only in 2003, are mysteriously large and complex, seemingly between bacteria and the tiny, simple viruses of classical biology. Scientists still don’t know much about what giant viruses do, other than kill amoebas and algae. Leave it to viruses, however, to keep surprising us: Giant viruses don’t just kill their hosts. In some cases, according to a recent study, they can keep their hosts alive and become part of them.

A couple of years ago, Monir Moniruzzaman, a postdoctoral researcher at Virginia Tech, was trying to unravel the evolutionary history of giant viruses. He stuck a particular viral gene into a large genomic search engine to scrounge up similar viruses, which he would then assemble into an evolutionary tree. To his surprise, his top match wasn’t a virus at all: It was algae.

As he kept searching for more viral genes and kept getting more algae hits, he and his adviser, Frank Aylward, noticed a strange pattern. The viral genes in the algae samples had been subtly altered, as if they were being passed down from generation to generation as part of the algae genome.

Giant viruses weren’t simply infecting and killing algae, it seemed; sometimes, they were integrating their DNA into the living algal cell’s DNA.Moniruzzaman and his co-authors ultimately found evidence of giant viruses integrating into 24 of the 65 genomes of green algae they studied. “It just kind of just blew up. We didn’t realize it was so common and happening to such extent,” Moniruzzaman says. In one alga, Tetrabaena socialis, a full 10 percent of its genes came from giant viruses.

All of this suggests that giant viruses play an important role in driving the evolution of their host species—not just by preying on the weak but also by supplying new genes. “We have a tendency to always think of viruses as being detrimental, especially now,” during a pandemic, says Chantal Abergel, a virologist at the French National Centre for Scientific Research who was not involved in the study.

But virus-host relationships can be more complicated. A group of viruses called retroviruses, for example, integrated into the genomes of human ancestors long ago, and its genes are now used to create the placenta during pregnancy. Integrated giant-virus genomes might serve as a similar source of new genes for their single-celled hosts.

What’s unusual about the giant-virus integrations is how big they are. Giant viruses are physically bigger than conventional viruses, and their genomes are substantially longer and more complex. The largest giant virus has a genome of a whopping 2.5 million base pairs. (In comparison, the genome of the coronavirus that causes COVID-19 is only about one-80th as long.) “Just the size of some of these integrations is remarkable,” says Curtis Suttle, a virologist at the University of British Columbia, who was not involved in the study.

The integrations may have occurred during persistent infections, which scientists have sometimes observed with giant viruses they grow in their labs. In these cases, the giant virus never quite overtakes the cell to kill it, but the cell also never manages to clear the virus. They exist in some sort of equilibrium. Perhaps during one of these long-term infections, the giant virus managed to paste its genome into the cell’s.

Moniruzzaman and Aylward found several changes in the viral genes in algae cells to suggest they were being passed down through the generations, and were not just contamination from a transient infection. Most tellingly, the viral genes contained “introns,” special sequences found only in complex cellular life, as if the algae had added them so those genes could be expressed. “It looked like the genes had actually been split in two,” Aylward says. Other molecular signatures—like specific patterns of DNA base pairs—also suggested that the viral sequences belonged to the algae genome.

“This is a very convincing picture,” says Matthias Fischer, a virologist at the Max Planck Institute, who was not involved in the study. Moniruzzaman’s study cannot prove that the viral genes serve any function in the algae; a natural follow-up experiment would study whether the viral genes are turned on in the algae or whether they simply lie dormant.

Much remains unknown about giant viruses as a group. On the basis of the few pieces of the giant-virus puzzle already put together, Suttle estimates that scientists have cataloged only “a small fraction of a percent” of the diversity out there. “So almost nothing,” he adds.

Moniruzzaman is now looking for more examples of DNA integration across a broad swath of single-celled organisms, such as fungi and protists, that also might be infected by giant viruses. “The eye-opener from this study,” says Fischer, “is that again we were limited by our own expectations.” No one had ever expected that giant viruses could integrate into host genomes, so no one had ever looked.
Newsletter

Related Articles

0:00
0:00
Close
Severe Heatwave Claims 2,300 Lives Across Europe
NVIDIA Achieves Historic Milestone as First Company Valued at $4 Trillion
Declining Beer Consumption Signals Cultural Shift in Germany
Linda Yaccarino Steps Down as CEO of X After Two Years
US Imposes New Tariffs on Brazilian Exports Amid Political Tensions
Azerbaijan and Armenia are on the brink of a historic peace deal.
Emails Leaked: How Passenger Luggage Became a Side Income for Airport Workers
Polish MEP: “Dear Leftists - China is laughing at you, Russia is laughing, India is laughing”
BRICS Expands Membership with Indonesia and Ten New Partner Countries
Weinstein Victim’s Lawyer Says MeToo Movement Still Strong
U.S. Enacts Sweeping Tax and Spending Legislation Amid Trade Policy Shifts
Football Mourns as Diogo Jota and Brother André Silva Laid to Rest in Portugal
Labour Expected to Withdraw Support for Special Needs Funding Model
Leaked Audio Reveals Tory Aide Defending DEI Record
Elon Musk Founds a Party Following a Poll on X: "You Wanted It – You Got It!"
London Stock Exchange Faces Historic Low in Initial Public Offerings
A new online platform has emerged in the United Kingdom, specifically targeting Muslim men seeking virgin brides
Trump Celebrates Independence Day with B-2 Flyover and Signs Controversial Legislation
Boris Johnson Urges Conservatives to Ignore Farage
SNP Ordered to Update Single-Sex Space Guidance Within Days
Starmer Set to Reject Calls for Wealth Taxes
Stolen Century-Old Rolls-Royce Recovered After Hotel Theft
Macron Presses Starmer to Recognise Palestinian State
Labour Delayed Palestine Action Ban Over Riot Concerns
Swinney’s Tax Comments ‘Offensive to Scots’, Say Tories
High Street Retailers to Enforce Bans on Serial Shoplifters
Music Banned by Henry VIII to Be Performed After 500 Years
Steve Coogan Says Working Class Is Being ‘Ethnically Cleansed’
Home Office Admits Uncertainty Over Visa Overstayer Numbers
JD Vance Questions Mandelson Over Reform Party’s Rising Popularity
Macron to Receive Windsor Carriage Ride in Royal Gesture
Labour Accused of ‘Hammering’ Scots During First Year in Power
BBC Head of Music Stood Down Amid Bob Vylan Controversy
Corbyn Eyes Hard-Left Challenge to Starmer’s Leadership
London Tube Trains Suspended After Major Fire Erupts Nearby
Richard Kemp: I Felt Safer in Israel Under Attack Than in the UK
Cyclist Says Police Cited Human Rights Act for Riding No-Handed
China’s Central Bank Consults European Peers on Low-Rate Strategies
AI Raises Alarms Over Long-Term Job Security
Saudi Arabia Maintains Ties with Iran Despite Israel Conflict
Musk Battles to Protect Tesla Amid Trump Policy Threats
Air France-KLM Acquires Majority Stake in Scandinavian Airlines
UK Educators Sound Alarm on Declining Child Literacy
Shein Fined €40 Million in France Over Misleading Discounts
Brazil’s Lula Visits Kirchner During Argentina House Arrest
Trump Scores Legislative Win as House Passes Tax Reform Bill
Keir Starmer Faces Criticism After Rocky First Year in Power
DJI Launches Heavy-Duty Coaxial Quadcopter with 80 kg Lift Capacity
U.S. Senate Approves Major Legislation Dubbed the 'Big Beautiful Bill'
Largest Healthcare Fraud Takedown in U.S. History Announced by DOJ
×