Researchers were able to find some distinct virus-like entities in the human mouth and gut.
Viroids
Scientists were able to find virus-like entities that were never seen before hiding in the human mouth and gut. These viroids could affect human microbiome gene activity.
The researchers were able to confirm one viroid host, a common mouth bacterium known as Streptococcus sanguinis. They have yet to confirm more hosts. However, they think that at least a fraction of these are bacteria.
Viroids are small RNA loops that have been found to primarily infect plants. They are different from RNA-based and larger viruses in various ways.
For one, these viroids are naked and do not have protective shells that viruses typically make use of to hold their genetic material. Their RNA also does not have protein-building instructions. Viruses, on the other hand, have instructions for their exterior shells and for some enzymes that they must replicate. Viroids co-opt the enzymes for their own hosts.
Though viruses were initially believed to just infect plants, studies show that they can also infect other hosts, such as fungi, bacteria, or animals. In the new study, researchers looked for possible viroids among microbe genes within the body of humans.
Obelisks Viroids
In the recent report "Viroid-like colonists of human microbiomes" that is still in a preprint database, scientists were able to introduce Obelisks, which is a new viroid class they found in the gut and mouth of humans. The were able to identify almost 29,960 viroid samples.
They named the viroids Obelisks due to the secondary structure of the viroids, which is a 3D shape that the researchers assumed to be folding on themselves. This secondary structure is predicted to have a thin rod's appearance.
With previously published data, the researchers looked through gene activity readouts in various communities of microbes in the body. These summaries of gene activity are called metatranscriptomes.
The researchers observed the presence of Obelisks in around 7% of metatranscriptomes from the feces of humans. The samples of stool offer a glimpse of gene activity within the gut microbiome. They also found the Obelisks in around 53% of the screened metatranscriptomics of the mouth.
Through further analyses, the researchers were able to match the viroid with its S. sanguinis host. They note that, though they do not know other Obelisk hosts, it is reasonable to think that at least a fraction can be found within bacteria.
Some Obelisks were also observed to have instructions necessary for enzyme replication. This makes them even more complex compared to the previous description of viroids. However, like several viroids, they lacked instructions for the outer layer.
Whether these viroids do or do not impact human health remains unknown. However, they could shape the human microbiome. There is also a continuing discussion of whether viroids evolved from viruses or vice versa. The discovery could aid in this discussion.
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