A few months ago, scientists discovered previously unseen organisms in the digestive system. We continue to discuss what it is

• They were called obelisks because of the shape that these RNA structures take.

• They can be considered an intermediate link between viruses and other very similar organisms: the so-called “viroids”.

When we try to define life, we often think of viruses—organisms with some of the characteristics of living things that are not fully living things. Now we may have discovered another organism on this edge of life: obelisks.

Along the obelisk path. A few months ago, a group of scientists announced a strange discovery: the genetic remains of a hitherto unknown organism. And he did this no less than by studying the microbiome of the human digestive system.

The genetic material sequences are symmetrical and elongated rod-shaped strands of RNA. Hence the name chosen for them – obelisk. However, these are short genetic chains about 1000 nucleotides long.

Between viruses and viroids. This makes obelisks very simple, more so than viruses. The latter are capable of encoding proteins that encapsulate genetic material, giving them the appearance of another cell. However, the obelisk will have nothing but genetic information that will live and reproduce inside some bacteria.

This lack of an outer “layer” is reminiscent of another organism on the border of life and non-existence – viroids. These viroids are non-coding genetic chains (they do not produce proteins themselves) but interact with the plant cellular genome. On the other hand, the RNA of the obelisks could code for some proteins.

Our tenants. Early research suggests that these organisms will be relatively common in the human microbiome, with about 10% of samples analyzed showing evidence of these organisms. In one of the databases the team studied, which contained samples of participants’ oral microbiomes, about 50% of the samples contained this genetic material.

In addition to the mouth, these obelisks have been found in other areas of the human gastrointestinal tract. It is clear that different types of obelisks can be found in different microbial “ecosystems.” The team identified almost 30,000 sequences, each of which could be classified as an obelisk type.

Colonizing bacteria. The next step was to find this genetic information in the primary host, bacteria. The obelisks appear to have “colonized” our microbiome through bacteria.

And the team found its trace in bacteria of the species Streptococcus blood

. These bacteria are often found in our mouths. The team analyzed this bacterium and found genetic information matching the obelisk: an RNA sequence 1,137 nucleotides long.

Obelisks and oblins. Genetic information can be understood as a mechanism for protein production. The proteins encoded by these genes are called oblins.oblins). We know, as stated earlier, that these proteins are not used to encapsulate the genetic information of this organism, but there is even more that we do not know about these proteins, two types of which are already known (Oblines 1 and 2). .

Much remains to be investigated. These findings are still under discussion in the scientific community. They have not yet been published in any journal, but draft articles are available for those wishing to view the details in the repository. BiorXiv.

If these results are confirmed, we will be able to better understand the evolution of viruses and especially viroids. Until now, we believed that the latter infect only plants. However, the discovery of such an organism hidden in plain sight within our own microbiome suggests that we still have a lot to learn about our own inner lives.

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Image | growing Streptococcus sanguinis.

Ajay Kumar Chaurasia