New virus-like entity discovered – “Obelisk” explanation

Analysis – Biological entities called obelisks lurk in large numbers in the human mouth and intestines. Recently discovered by a team at Stanford University, these microscopic entities are circular pieces of genetic material that contain one or two genes and self-assemble into rod-like shapes.

Although the study is still in preprint status, meaning it has not been peer-reviewed, it has already been widely written about, including in two leading journals: Nature and Science.

Let's delve deeper into the mysterious world of tiny “life forms.”

In biology, as in physics, things can get stranger and the rules more vague as the scale gets smaller and smaller.

Since viruses cannot reproduce without the help of a host, they can most generously be considered to be on the verge of what constitutes life. However, an estimated 1 billion individual viruses (one followed by 31 zeros) are found on Earth in every conceivable habitat, and through infection and manipulation of hosts, they have probably influenced the evolutionary trajectory of all life. It is thought that it has had an influence on.

Viroids take a deeper look into the world of microscopic biological entities. It is a small piece of genetic material (a DNA-like molecule known as RNA) that cannot make proteins and, unlike viruses, does not have a protective shell surrounding its genome. .

Viroids are an example of ribozymes. RNA molecules may be distant echoes of the first self-replicating genetic elements from which cellular life originated.

Viroids can self-cleave (chop up) and rejoin (put back together) their genomes as part of their replication cycle. And despite their simplicity, they can cause serious diseases in flowering plants.

Between viruses and viroids – perhaps

The new preprint describes “viroid-like colonizers of the human microbiome.” If “viroid-like” sounds vague, that's entirely intentional. The newly discovered biological entity falls somewhere between a virus and a viroid.

In fact, the name obelisk was chosen not only because of its shape, but also to give it some leeway in case it turns out to be more similar to RNA plasmids (a different type of genetic element present within bacteria) than to viruses or viroids. It was also proposed to

Like viroids, obelisks have circular, single-stranded RNA genomes and lack a protein coat, but like viruses, their genomes contain genes predicted to encode proteins.

All obelisks described so far encode a single major protein known as obelin, and many encode a second, smaller obelin.

Obrin has no evolutionary similarity, or “homology,” to other proteins found, and we have few clues about its function.

By analyzing existing datasets from human intestines, mouths, and a variety of other sources, the Stanford University team discovered approximately 30,000 different obelisk types.

The genomes of these obelisks have been overlooked until now because they are very unlike anything previously described. The Stanford team discovered that they used an ingenious custom method to search a database of single-stranded circular RNA molecules for viroid-like elements.

From their results, it is clear that obelisks are not uncommon. Researchers discovered them in a variety of niche datasets from around the world.

These elements were detected in approximately 7% of microbiome datasets from the human gut and 50% of datasets from the mouth. However, it is unclear whether these datasets accurately represent the prevalence and distribution of obelisks.

Different types of obelisks were found in different body parts and from different donors. Long-term data has revealed that people can keep his one type of obelisk for about a year.

The obelisk likely relies on microbial host cells to replicate, including cells that replicate within the human body. Bacteria or fungi may be the hosts, but exactly which species harbor these elements is unknown.

However, researchers found that the common bacterial components of dental plaque streptococcal bloodwhich serves as a host for certain obelisk types.

Enemy or ally?

as S's blood Obelisks are easy to grow and experiment with in the laboratory, making them a valuable model for understanding the basics of obelisk biology.

This is extremely important because nothing is known about the broader evolutionary and ecological significance of the obelisk. They can be parasitic and harmful to the host cell, or they can be beneficial.

The host may have evolved elaborate defense mechanisms against obelisks, or may have actively mobilized obelisks to gain an unexpected advantage. If the obelisk changes or disrupts the human microbiome, it could in turn affect human health and may even have therapeutic potential.

Alternatively, the obelisk may cause neither harm nor benefit to its microbial or human hosts. Rather, it may simply exist as a stealth evolutionary passenger, silently replicating endlessly, like the original “selfish gene.”

* Ed Fell is Professor of Microbial Evolution at the Milner Center for Evolution at the University of Bath.