An international group of scientists, led by Nobel Prize winner Andrew Fire and with the participation of the Institute of Molecular and Cellular Biology of Plants (IBMCP) – a joint center of the Universitat Politècnica de València (UPV) and the Higher Council for Scientific Research ( CSIC), an organization dependent on the Ministry of Science, Innovation and Universities (MICIU) – has discovered a new biological entity in bacteria present in the human mouth and intestines.
This entity has been called “Obelisk” due to its structure and is an infectious agent whose genome is even simpler than that of viruses, although its function and impact on health are not yet understood. The discovery has been achieved through bioinformatics analysis of genetic sequences extracted from human fecal samples and opens questions about microbial evolution and diversity. The study has just been published in the journal Cell.
The human microbiome is a vast microbial ecosystem that hosts an impressive diversity of microorganisms, such as viruses, bacteria, fungi and protozoa, which play an essential role in functions such as digestion and immune response. As knowledge about this complex web of microscopic life expands, fundamental aspects of its impact on health are being revealed.
In this context, a multidisciplinary team led by Andrew Fire at Stanford University (USA), together with CSIC researchers such as Marcos de la Peña at the IBMCP in Valencia and the University of Toronto (Canada), has revealed the existence of Obelisks, tiny biological entities never previously observed, which introduce a new complexity into the universe of the human microbiome.
Implications of Obelisks for health and biology
Obelisks are infectious agents with a circular RNA genome of just 1,000 nucleotides, which is why they are considerably smaller in size than many viruses. As explained by CSIC researcher Marcos de la Peña, in an article published by this organization: “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. ”. “They lack the protein coat that characterizes viruses, but, like viruses, they are capable of encoding proteins,” he adds.
De la Peña also mentions that Obelisks have similarities with viroids, a class of infectious agents that affect plants and that share with them the circular RNA genome and self-cutting ribozymes. However, plant viroids are even simpler, with a size of 300 to 400 nucleotides and no ability to encode proteins. Thus, Obelisks represent an intermediate point between viruses and viroids, posing a challenge for their classification and understanding.
“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 discovery of these entities was possible thanks to bioinformatic studies of genetic sequences derived from human stool samples, which detected Obelisk RNA in 7% of the 440 subjects analyzed. Additionally, additional studies identified around 30,000 species of Obelisks in biological samples from various parts of the world, including soils, oceans, and animal microbiomes. A particular strain of Streptococcus sanguinis, a common bacteria in the oral microbiota, presents a notable accumulation of these RNAs, found in approximately half of the oral samples studied.
The exact function of Obelisks and the proteins they encode remains unknown. The remarkable accumulation of RNA in bacteria suggests a possible role in the regulation of cellular activity, with possible implications for human health, given the role of the microbiome in fundamental physiological functions, such as digestion and immunity.
This finding also raises profound questions about the origin and evolution of viruses and microbial diversity. As De la Peña comments, “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.”
Source: Higher Council for Scientific Research (CSIC)
