Space viruses may indicate alien life

(ORDO NEWS) — You probably only think about viruses when you’re sick, but a group of microbiologists wants to change that. In fact, they want you to think that viruses can be found in space.

In a recent review published Jan. 10 in the journal Astrobiology, a trio of US and Japanese scientists suggested that viruses could be spreading through interplanetary space. These researchers want to convince astrobiologists to spend more time looking for these curious molecular machines.

The virion, the form that the virus takes outside the host, consists of genetic material enclosed in a protein coat. Some viruses also have an outer lipid layer called the envelope. The virion can be thought of as a seed or spore, the authors write. [7 everyday things that strangely happen in space].

Viruses are beyond the definition of life. They have no mechanisms to reproduce on their own, so they must infect the host cell and take over its mechanisms. This has led to decades of debate about whether viruses should technically be considered alive.

But for the authors of the review of reproductive methods, viruses are enough. Indeed, “when the entire replication cycle of a virus is considered, it approximates NASA’s working definition of life: “a self-sustaining chemical system capable of Darwinian evolution,” the review says.

If scientists discovered the virus in space – perhaps on a meteor – few would argue that this discovery is not proof of the existence of life in space, the authors write.

Why don’t scientists explore the Martian surface, the lakes of Titan, or the geysers of Enceladus for evidence of these tiny “life forms”?

Partly because the technology to do so is still under development, says senior review author Kenneth Stedman, professor of biology at Portland State University.

Scientists are currently looking for chemical signatures that can be used to identify viruses in fossils. But if they can’t find viruses in really ancient rocks on Earth, they can’t do it in really ancient rocks on Mars or Titan, he said.

Viruses are not metabolically active on their own, so they produce few by-products. Lipids in virus envelopes are currently a prime candidate for a virus biomarker, as these compounds can persist for hundreds of millions of years, Steadman told Live Science. But scientists have yet to establish that these molecules are unique to viruses and do not exist in any cellular organism.

Currently, scientists can identify viruses by examining the structure of their shells using electron microscopes. But so far there is no way to install these powerful instruments on the rover. And given the diversity of virus forms on Earth, Steadman said he doubted scientists would even be able to recognize the form of an alien virus.

Here on Earth, viruses are an essential part of life, Stedman says. First, viruses are ubiquitous. The oceans alone contain approximately 10^31 individual virions. This is about 1 million times more than the number of stars in the observable universe. Viruses are an integral part of most nutrient cycles on our planet.

What’s more, viruses and cells have co-evolved almost since life began on our planet, Stedman says. Cells evolving to resist their viral invaders give rise to new forms and behaviors.

And viruses transfer genes between unrelated cells, which scientists call horizontal gene transfer. While this process has led to a huge variety of life on Earth, it muddies the waters for researchers tracking the evolution of viruses. “If there’s even a little water in the mud, you’re in luck,” Stedman says.

Scientists know that viruses use both RNA and DNA to encode their genetic information, in single- and double-stranded forms, Stedman said. All known cellular organisms use double-stranded DNA, which is why some scientists believe that viruses may be remnants of ancient life forms that existed before DNA existed.

All this suggests that “life on Earth would be very different if there were no viruses,” Steadman said.

Currently, scientists can only determine cellular life. In addition to helping scientists learn more about our origins, developing ways to identify viruses is good practice for recognizing other, new life forms we might encounter, Steadman said. It’s important to keep an open mind when looking for life, as many habitats are very different from Earth’s.

“What is life? Are viruses alive? If we find viruses [in space], is that evidence of life? And will it be life as we know it, or life as we don’t know it?” Steadman asked. “We hope that we will make people think about these definitions.”


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