The human gut is home to a diverse community of microorganisms, including bacteria, fungi, viruses, and protozoa. These microbes play crucial roles in digestion, immune function, and overall health. Hence continuous studies and researches are underway to discover more of such species and their functions.

In a new study a previously unreported class of virus like elements called “Obelisks” are discovered in human gut metatranscriptomic data.

It is also observed that Obelisks form their own distinct phylogenetic group with no detectable sequence or structural resemblance to known biological agents.

Obelisks are prevalent in tested human microbiome meta transcriptomes with representatives detected in ∼7% of analysed stool meta transcriptomes (29/440) and in ∼50% of analysed oral metatranscriptomes (17/32). Obelisk compositions appear to differ between the anatomic sites and are capable of persisting in individuals, with continued presence over >300 days observed in one case.

“Obelisks” are observed to have apparently circular RNA ∼1kb genome assemblies, rod-like secondary structures encompassing the entire genome, and open reading frames coding for a novel protein superfamily, which we call the “Oblins".

According to data provided by NCBI it is found that a subset of Obelisks harbour Obelisk-specific hammerhead ribozyme motifs. Querying 5.4 million public sequencing datasets, we identified 29,959 distinct Obelisks (90 % ID threshold) present across ~220,000 datasets representing diverse ecosystems beyond the human gut microbiome (hGMB).

Approx. 30,000 Obelisks were discovered with 90% nucleotide identity on large scale researches conducted across several continents and various ecological niches.

From this search, a subset of Obelisks are identified to code for Obelisk-specific variants of the hammerhead type-III self-cleaving ribozyme.

A bacterial species (Streptococcus sanguinis) in which a subset of defined laboratory strains harboured a specific Obelisk RNA population was also discovered by the researchers. It represented the  Obelisk-Host pair, with Streptococcus sanguinis acting as a replicative host.

This new biological entity found in the human gut shows characteristic properties that resemble somewhere with both viruses and viroid's. Like viroids , obelisks have a circular single-stranded RNA genome and no protein coat but, like viruses, their genomes contain genes that are predicted to code for proteins etc.

Although the study is still in preprint form that means it has not been peer-reviewed but still is extensively talked and written about.

References;

1. Zheludev, I. N., Edgar, R. C., Lopez-Galiano, M. J., de la Peña, M., Babaian, A., Bhatt, A. S., & Fire, A. Z. (2024). Viroid-like colonists of human microbiomes. bioRxiv : the preprint server for biology, 2024.01.20.576352. https://doi.org/10.1101/2024.01.20.576352

2. Ivan N. Zheludev, Robert C. Edgar, Maria Jose Lopez-Galiano, Marcos de la Peña, Artem Babaian, Ami S. Bhatt, Andrew Z. Fire Viroid-like colonists of human microbiomes bioRxiv 2024.01.20.576352; doi: https://doi.org/10.1101/2024.01.20.576352

3. Thompson, Joanna. “Weird ‘Obelisks’ Found in Human Gut May be Virus-Like Entities.” Scientific American, February 20, 2024. https://www.scientificamerican.com/article/weird-obelisks-found-in-human-gut-may-be-virus-like-entity/.

4. Sidik, Saima. “‘Wildly weird’ RNA bits discovered infesting the microbes in our guts.” Nature, January 29, 2024. https://doi.org/10.1038/d41586-024-00266-7.

(Input from various sources)

(Rehash/Tushar Pandey/MSM)