They discover a new biological entity that lives in the human body

Scientists have discovered an unknown biological entity in the human microbiome that they have called “obelisk.” It is not a virus, bacteria or anything like that.

The research in which this astonishing discovery was made is the work of an international team led by Nobel Prize winner Andrew Fire and in which the Institute of Molecular and Cellular Biology of Plants (IBMCP), a joint center of the Polytechnic University of Valencia (UPV), participates. ) and the Higher Council for Scientific Research (CSIC), in Spain.

The microbiome is a complex microbiological ecosystem that resides in our bodies. It hosts an astonishing diversity of microorganisms that includes everything from viruses and bacteria to fungi and protozoa. We increasingly know more about this intricate biological network and its crucial role in health, intervening in functions as varied as digestion, the immune system or even our own behavior.

Now, in the aforementioned study, signed, among others, by Ivan Zheludev and Andrew Fire, both from Stanford University in the United States, as well as Marcos de la Peña, from the IBMCP, an additional layer of complexity in our world has been revealed. microscopic interior: obelisks, minimal biological entities never seen before and that challenge our understanding of the limits of life.

Obelisks are novel infectious agents with a tiny circular RNA genome of only a few thousand nucleotides, far below the RNA genomes that some viruses use to reproduce. “These RNA circles are highly self-complementary, which allows them to adopt a stable rod-shaped structure reminiscent of the Egyptian monuments that give them their name,” explains Marcos de la Peña. “They lack the protein coat that characterizes viruses, but, like viruses, they are capable of encoding proteins,” points out the CSIC researcher.

As a scientist who works at a plant research center, de la Peña points out that the obelisks are reminiscent of viroids, a family of subviral agents that infect plants and with which they share the circular RNA genome and the usual presence of self-cutting ribozymes. . “However, plant viroids are even tinier, about 300 or 400 nucleotides, and do not code for proteins. For all these reasons, the obelisks are halfway between viruses and viroids, which poses a challenge to their origin and classification,” says the researcher.

The discovery of the obelisks has been possible thanks to bioinformatics studies of genetic sequences obtained from human feces, the presence of these RNAs being detected in 7% of the 440 subjects analyzed. Massive bioinformatics analyzes also allowed the discovery of nearly 30,000 species of obelisks in biological samples collected throughout the planet, both in natural ecosystems (soils, rivers, oceans…) and in wastewater or animal microbiomes. Among all these data, it was detected that a strain of Streptococcus sanguinis, a common commensal bacteria in the microbiota of our mouth, accumulates obelisks in a very abundant way, finding that around half of the analyzed population contained obelisks in their oral cavity.

Recreation of intestinal bacteria (orange cells) infected by obelisks (black rods). (Image: IBMCP / CSIC / UPV)

The function and effects of obelisks and the proteins they encode is still a mystery, as the researchers emphasize. The high accumulation of RNA genomes inside bacteria would indicate, according to scientists, a possible role in the regulation of cellular activity with significant implications for health, since the microbiomes where these bacteria live influence numerous physiological aspects, from digestion to the immune system.

Furthermore, the discovery of the obelisks raises fundamental questions about the origin and evolution of viruses and microbiological diversity. According to De la Peña, “this discovery shows that the microbial world is much more complex than we imagined. “We have opened a door to a whole new field of exploration that can revolutionize our understanding of virology, biology and even the very origin of life on Earth.”

The study is titled “Viroid-like colonists of human microbiomes.” And it has been published in the academic journal Cell. (Source: Isidoro García / CSIC)