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Updated: Jun 9, 2025

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Viroid-like colonists of human microbiomes.

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  • 1Stanford University, Department of Biochemistry, Stanford, CA, USA.

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Summary

Scientists discovered "obelisks," novel circular RNA elements with unique structures and genes. These prevalent RNA molecules were found in diverse environments, including the human microbiome, suggesting a significant, yet unexplored, biological role.

Keywords:
RNA metaviromicshepatitis delta virushuman microbiomeviroid

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Area of Science:

  • Molecular Biology
  • Microbiology
  • Genomics

Background:

  • Heritable RNA elements represent a poorly understood aspect of molecular biology.
  • The diversity and prevalence of non-coding and regulatory RNAs are increasingly recognized.

Purpose of the Study:

  • To describe a newly identified class of heritable RNA elements, termed "obelisks."
  • To characterize their genomic, structural, and phylogenetic properties.
  • To investigate their prevalence in global and human microbiomes.

Main Methods:

  • Bioinformatic analysis of RNA sequences and structures.
  • Phylogenetic analysis to determine evolutionary relationships.
  • Metatranscriptomic data analysis to assess prevalence in various environments.
  • Identification of a bacterial host for a specific obelisk.

Main Results:

  • Discovery of "obelisks": circular RNA molecules (~1 kb) with predicted rod-like structures and open reading frames encoding Oblin proteins.
  • Identification of a subset containing hammerhead ribozymes.
  • Obelisks form a distinct phylogenetic group.
  • Over 29,000 distinct obelisks identified globally.
  • High prevalence in human microbiomes (stool and oral).
  • Established Streptococcus sanguinis as a host for an obelisk, with non-essential maintenance for bacterial growth.

Conclusions:

  • Obelisks represent a novel, diverse class of heritable RNA elements.
  • They have colonized various ecological niches, including the human microbiome, largely unnoticed.
  • Further research is needed to determine the functional impact and biological significance of obelisks.