3 Minutes
Scientists have uncovered a previously unknown class of tiny RNA-based entities living inside bacteria that inhabit our mouths and guts. These rod-shaped, circular RNAs—nicknamed 'obelisks'—are smaller than many viruses but carry genetic instructions that cells can read. The discovery raises fresh questions about how much of our internal ecosystem remains unseen and what these micro-architectures might mean for human health.
What are obelisk RNAs and why they're unusual
Researchers at Stanford describe obelisk RNAs as circular, single-stranded RNA molecules roughly the size of viroids but with a rod-like self-organized structure. Unlike classic viruses, obelisks lack a protein coat. Yet some of their genomes include one or two genes that appear capable of encoding proteins—making them biologically ambiguous: part viroid, part virus.
How scientists found almost 30,000 types
The team detected nearly 30,000 distinct obelisk sequences across global microbiome samples, with the highest prevalence in oral and gut communities. Using large-scale metagenomic sequencing and targeted bioinformatics searches for small circular RNAs, investigators mapped these elements across diverse human populations. As Ed Feil, a microbial evolution expert, explains, obelisks look like circular genetic scraps that self-organize into rods and may colonize bacterial and fungal cells.
Why microbiologists are both excited and cautious
'It's insane,' said Mark Peifer, a cell and developmental biologist, reflecting the surprise many researchers feel at the scale of the finding. The immediate questions are practical: which host cells support obelisk replication, how do they interact with bacteria and fungi, and can they transfer functional information to host cells? Their ability to 'transmit instructions'—in the sense that their RNA can be read by cellular machinery—makes these elements intriguing candidates for both ecological impact and future study.
How obelisks compare to viruses and viroids
- Viroids: minimal plant pathogens composed of naked circular RNA that do not encode proteins.
- Viruses: genome plus protein coat, often encoding multiple proteins and relying on host machinery to replicate.
- Obelisks: circular, single-stranded RNAs without a protein coat but with gene-like sequences, placing them between viroids and viruses in complexity.
Implications and next steps for research
Scientists now face a puzzle: determine whether obelisks are harmless passengers, modulators of microbial behavior, or agents with potential to affect human health indirectly through the microbiome. Next steps include laboratory isolation, replication and infectivity assays, host-range experiments, and structural studies to understand how these RNAs form rod-like shapes.
The discovery expands the known genetic diversity in the human microbiome and highlights how much remains to be learned about microscopic genetic elements that influence microbial ecosystems. Whether obelisks will rewrite parts of virology or microbiome biology is still uncertain—but their ubiquity and novelty ensure they will be closely studied in the years ahead.
Source: popularmechanics
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