Amazing stuff!
"... Named after the highly-symmetrical, rod-like structures formed by its twisted lengths of RNA, the Obelisks' genetic sequences are only around 1,000 characters (nucleotides) in size. In fact, this brevity is likely one of the reasons we've failed to notice them previously. ...
In a study that has yet to be peer reviewed, ... team searched 5.4 million datasets of published genetic sequences and identified almost 30,000 different Obelisks. They appeared in about 10 percent of the human microbiomes the team examined.
In one set of data, Obelisks turned up in 50 percent of the patients' oral samples. What's more, different types of Obelisks appear to be present in different areas of our bodies. ..."
"The human microbiome just gained a new dimension: scientists have discovered tiny bits of RNA — even smaller than viruses — that colonize the bacteria inside human guts and mouths. Too minimal to be considered a standard life form, these scraps of genetic material are among the smallest known elements to transfer information that can be read by a cell, and the sequences that they encode are new to science. ..."
From the abstract:
"Here, we describe the “Obelisks,” a previously unrecognised class of viroid-like elements that we first identified in human gut metatranscriptomic data. “Obelisks” share several properties:
(i) apparently circular RNA ∼1kb genome assemblies,
(ii) predicted rod-like secondary structures encompassing the entire genome, and (iii) open reading frames coding for a novel protein superfamily, which we call the “Oblins”.
We find that Obelisks form their own distinct phylogenetic group with no detectable sequence or structural similarity to known biological agents. Further, Obelisks are prevalent in tested human microbiome metatranscriptomes with representatives detected in ∼7% of analysed stool metatranscriptomes (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. Large scale searches identified 29,959 Obelisks (clustered at 90% nucleotide identity), with examples from all seven continents and in diverse 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. Lastly, we identified one case of a bacterial species (Streptococcus sanguinis) in which a subset of defined laboratory strains harboured a specific Obelisk RNA population. As such, Obelisks comprise a class of diverse RNAs that have colonised, and gone unnoticed in, human, and global microbiomes."
‘Wildly weird’ RNA bits discovered infesting the microbes in our guts Rod-shaped structures named ‘obelisks’ are even smaller than viruses but can still transmit instructions to cells.
Viroid-like colonists of human microbiomes (open access)
Figure 1. Obelisk alpha has a predicted extensive secondary structure and appears to colonise and speciate within the human gut
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