3D render of the human gut. Image: Oleksandra Troian vi
Scientists have discovered strange entities hiding in our guts and mouths that may represent an entirely new class of life—if they are even alive.Dubbed “obelisks,” these tiny rings of RNA can fold into a structure that looks more like a rod, hence the name. They’re also surprisingly commonplace in our microbiomes—the community of viruses, bacteria, fungi, and their genes that live in our bodies. Yet, they’ve gone undetected until now and represent the latest discovery in an ever-growing list of mysterious “genetic agents” hiding in plain sight. Indeed, the researchers who discovered them report that their function, if they have one, is a mystery.
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The obelisks were discovered by a team lead by Nobel Prize-winning geneticist and pathologist, Andrew Fire, who shared their findings in a preprint. Using a genome-hunting filter they developed, researchers found just shy of 30,000 obelisks by scouring the Integrative Human Microbiome Project database, a dataset of microbiomes used by researchers worldwide to study human health and disease. When they searched other microbiome datasets from all over the world, they uncovered even more. In one dataset, 6.6 percent of gut samples and a whopping 53 percent of mouth samples contained obelisks. “The prevalence and apparent novelty of these elements implies more is yet to be learned about their interplay with microbial and human life,” the authors write. Fire has previously declined to be interviewed, given that the finding still needs to be scrutinized by the scientific community in peer review. Obelisks represent their own class of organism (if you can even call them that—the paper refers to them as "biological entities"). They lie somewhere between viruses and viroids—single-stranded, circular RNA that were thought to mostly infect plants, including wreaking havoc on weed crops. Although they look pretty similar, viroids can’t make proteins of their own, whereas researchers discovered that obelisks can. These obelisk-made proteins aren’t like any proteins we know about today, which is why Fire’s team named them “oblins.” Exactly what these oblins do for obelisks is just one of a plethora of questions researchers now have.Viruses, too, can make their own proteins, but they have a protective shell surrounding their genetic material, unlike obelisks. Obelisks, therefore, need some kind of host. The researchers managed to identify one: A bacterium called Streptococcus sanguinis that lives mostly in dental plaque in our mouths. Exactly which other hosts obelisks inhabit is yet another mystery, as are what they do to their host and how they spread. In the past three years scientists have discovered tens of thousands of new viroid-like entities. It’s made them completely re-evaluate how they classify the microscopic world, how these things evolved, and just how small and basic reproducing entities can be. It’s still debatable whether viruses are alive, let alone something smaller and simpler.“It’s insane,” Mark Peifer, a cell and developmental biologist at the University of North Carolina at Chapel Hill, told Science. “The more we look, the more crazy things we see.”