Hundreds of Mysterious Giant Viruses Lurking in the Ocean Discovered

Scientists have discovered hundreds of mysterious giant viruses lurking in the ocean. It sounds like something out of the latest sci-fi blockbuster. But scientists at the University of Miami have warned that the world's oceans are indeed teeming with "giant viruses," also known as gyrus.

Most viruses are less than 0.5% the thickness of a human hair – too small to be seen with the naked eye, writes the Daily Mail. In this case, however, the researchers claim that the giant viruses are five times larger, rivaling bacteria in size. Remarkably, all 230 giant viruses were previously unknown to science. Moreover, their impact on humans remains unclear.

Giant viruses typically infect tiny organisms such as algae and amoebae that live in the world's waterways, although they can also live on land. "The impact of giant viruses is certainly felt in all habitats, but there has been particular interest in identifying their impact on aquatic ecosystems," experts say.

Most viruses are between 20 and 200 nanometers in size, but giant viruses can exceed 1,000 nanometers. For comparison, a human hair is about 80,000 to 100,000 nanometers thick. Giant viruses, as the Daily Mail reports, were virtually unknown to science until the early 21st century, but scientists believe they could have a major impact on life on Earth.

In the oceans, they infect various species of single-celled algae, photosynthetic organisms that are responsible for about half of Earth’s oxygen production. This viral infection can cause the rapid collapse of algal blooms – clumps of algae that stretch across the ocean for tens of thousands of kilometers – which in turn can have significant impacts on vast marine, atmospheric, and terrestrial ecosystems.

While algae blooms can cause excessive growth and become a problem, giant virus infections can cause the opposite problem - causing them to collapse quickly, which can deplete oxygen in the atmosphere.

Where and what types of these giant viruses exist around the world is still unknown, the researchers note. To learn more, they used the computer program BEREN to identify the genomes of microbes in seawater samples. Most of the giant viruses they found were either algaviruses (135) or imitviruses (81). The algae, which are typically between 100 and 200 nanometers in diameter, get their name from their ability to specifically infect photosynthetic, single-celled eukaryotes known as seaweed.

Meanwhile, "genetically complex" imitoviruses have a flexible genetic strategy that potentially allows the virus to survive in a wider range of hosts.

Because giant viruses contain huge amounts of genetic material – up to 100 times more than other viruses – some are better able to manipulate their hosts when they infect. This is one reason why giant viruses are considered more dangerous than normal-sized viruses, although the factors that make one virus more deadly than another are varied and complex, the Daily Mail points out.

"Giant viruses possess genes involved in cellular functions such as carbon metabolism and photosynthesis that are traditionally found only in cellular organisms," said study author Benjamin Minch of the University of Miami. "This suggests that giant viruses play an outsized role in manipulating their host's metabolism during infection and influencing marine biogeochemistry."

Another classification of giant viruses, called Pimascovirales, includes the largest known virus, the pithovirus, which is 1,500 nanometers long. Pithovirus, discovered more than a decade ago in Siberian permafrost, is thought to have been there for 300,000 years and is still capable of infecting living organisms.

Most giant viruses (108) were found in the Baltic Sea, a large brackish body of water between the Scandinavian Peninsula and the rest of continental Europe, followed by Antarctica (65).

But others have been found in the Arctic, South Pacific, North Atlantic, Sargasso Sea (a special area of ​​the North Atlantic Ocean) and Korea’s Changmok Bay. Overall, this suggests that colder marine environments are a richer reservoir of giant viruses, many of which are likely yet to be discovered. Cold-adapted marine giant viruses may now be threatened by climate change, further complicating the picture.

A new study published in the journal Nature npj Viruses provides more insight into these little-studied microorganisms. Further research could help to determine where giant viruses live on land, or whether they are restricted to remote, sparsely populated areas.

"This research has allowed us to build a foundation for improving existing tools to detect new viruses that could help us monitor pollution and pathogens in our waterways," said Benjamin Minch.