Researchers at France's Aix-Marseille University are accustomed to finding new giant viruses. But they say their latest discovery – a virus that dwarfs all others – is unlike anything they've seen before.

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Dr Chantal Abergel is not easily surprised by the discovery of giant viruses. A director of research at Aix-Marseille University and the CNRS (France’s National Centre for Scientific Research), she has already been involved in identifying two very large viruses, the Mimivirus and Megavirus.

In fact, the IGS laboratory headed by her colleague, Professor Jean-Michel Claverie, had long predicted the existence of giant viruses. And yet they were taken aback by their own latest discovery... a virus so big that it resembled a cell.

“We were expecting giant viruses to have 1,000 genes; however, one of the two viruses we recently found had 2,556 genes, which is huge,” Dr Abergel told France24.com, adding that the other virus’s gene count was around 1,500.

The team at the IGS laboratory discovered the two viruses from samples obtained in Chile and Australia – two among several countries they were drawn to after earlier studies had pointed to the prevalence of giant viruses in marine environments.

“As far as Chile was concerned, we took advantage of Europe's ASSEMBLE project that allowed us to use their marine facilities worldwide to try different locations, one of which was Las Cruces, Chile. The sample in Australia was a result of random sampling we carry out in places we visit,” Dr Abergel explained.

Because of the unique nature of the viruses and the fact that little is known about their genetic makeup, Dr Claverie’s team opted for the term “Pandoravirus”.

A new perspective on evolutionary biology



“This discovery has opened a Pandora’s box,” said Dr Abergel. “It will force us to change the way we think about viruses. The Pandoraviruses are extremely complex. In fact, 90 percent of their genes are unlike anything we have known so far. Out of the 2,556 genes of the Pandoravirus, less than 200 are known to us. This discovery is bound to make us reconsider our perception of evolutionary biology.”

According to the French researcher, the Pandoravirus is totally different from previously known viruses.

“Normally, under a microscope, viruses look like crystals. But Pandoraviruses looked like cellular structures. First, we thought they might be special bacteria because of their size and morphology. However, further tests confirmed that they were viruses,” she said.

When asked whether the French team’s discovery had set a new limit for a virus’s size, Dr Abergel replied that there was no limit. “Our latest discovery has shown that giant viruses exist all over the planet. To find Pandoraviruses at locations 15,000 km away from each other indicates the prevalence of such viruses,” she said.

While Pandoraviruses are not pathogenic to humans or animals, Dr Abergel said they were involved in the production of carbon and oxygen. “They have more than 2,000 genes whose nature and coding behaviour for proteins and enzymes is unknown to us. As a result, a deep study of such viruses will not only have important implications in the field of biotechnology, but it will also enhance our understanding of the beginning of life,” she said.



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