Viruses are entities that have to infect other cells in order to replicate. They may have genomes that are made of DNA or RNA. We are still discovering new types of RNA viruses, as shown in two new research reports. One has not yet been peer-reviewed, and characterizes a special kind of RNA virus that was found in the human mouth and gut. In another, unrelated new study that was reported in Nature Microbiology, scientists have described a novel RNA virus that was isolated from unique microbes that thrive in hot, acidic springs. These so-called thermoacidophilic bacteria host a virus that the researchers named HsRV.
The Nature Microbiology study may be the first to identify RNA viruses that can survive in environments where the temperatures get as hot as 70° Celsius to 80°C (158ºF to 176ºF). HsRV is also quite different from all other RNA viruses that are found in the two known RNA virus kingdoms, and suggests that there is another RNA virus kingdom that has not yet been described.
Additional research will be needed to learn more about HsRV. The researchers also have to find cells that this virus will infect, so the mechanisms that underlie the infection process, and the consequences of that infection can be elucidated. The investigators are also hoping to use the same approach to identify other novel RNA viruses that might live with animals, plants, or other microbes.
In an unrelated pre-print study posted on bioRxiv, scientists have reported the discovery of 'virus like entities' that live in the human mouth and gut microbiomes. These so-called obelisks, as named by the researchers who wrote the report, carry genomes that are made of RNA and form loops. The work suggested that about six percent of people carry obelisks in their guts and over half of us have them in our mouths.
The investigators behind this study have been searching for RNA genomes that have not yet been described. They have developed and used computational tools that scour existing genome databases in search of microbial genes that are active in humans. The tool focuses on RNA sequences that are likely to generate looped structures, just like the circular genomes that are found in viruses and viroids. Their genomes are similar to viroids though, because they do not seem to encode for anything resembling a viral capsule or shell. The genes these obelisks encode for don't seem to have anything in common with other known genes.
Scientists who were not involved in this study have called the results "insane," and "wildly weird."
This effort revealed about 30,000 sequence results, which all were around 1000 bases long, and represented a unique RNA sequence, or obelisk structure. Since RNA viruses tend to have longer genomes, the researchers concluded that these sequences may not be viruses. But they were found to encode for proteins that are related to RNA replication, so they could be more complex than viroids. The scientists noted that these obelisks may be a diverse type of RNA that have been flying under the radar, even though they live in microbiomes throughout our world. One thing about obelisks seems certain: we still have a lot to learn about these unusual entities and how they might affect humans.
Sources: University of Tsukuba, Nature Microbiology, bioRxiv