Unveiling a New Class of Viroids – “Obelisks” – in the Human Gut and Mouth

Scientists have recently uncovered a novel class of virus-like entities called “viroids” residing in the human gut and mouth. These viroids, termed “Obelisks,” have a potential impact on gene activity within the human microbiome.

Characteristics of Viroids

1. Nature of Viroids:
   • Viroids are tiny loops of RNA, a genetic relative of DNA.
   • Unlike larger RNA-based viruses, viroids lack protective shells for their genetic material.
2. Infection Mechanism:
   • Viroids infect plants, but recent studies suggest they may infect animals, fungi, or bacteria.
   • Viroids, unlike viruses, do not carry instructions for building proteins; they co-opt enzymes from their hosts.

Discovery of Obelisks: A New Class of Viroids

1. Host Identification:
   • The researchers confirmed Streptococcus sanguinis, a common mouth bacterium, as one host for Obelisks.
   • Additional hosts are suspected, with a likelihood that a fraction may be bacteria.
2. Characteristics of Obelisks:
   • Obelisks were identified in the human gut and mouth.
   • The 3D structure of Obelisks is predicted to resemble a thin rod.
3. Quantity and Preprint Status:
   • Nearly 29,960 examples of Obelisks were identified.
   • The findings were published on Jan. 21 in the preprint database bioRxiv and await peer review.

Gene Activity in Human Microbiome

1. Metatranscriptomes:
   • Researchers analyzed metatranscriptomes, summaries of gene activity in different microbial communities within the body.
   • Obelisks were found in 7% of human fecal metatranscriptomes and 53% of mouth metatranscriptomes.
2. Obelisks and S. sanguinis:
   • The team matched Obelisks with their host, Streptococcus sanguinis.
   • While the hosts of other Obelisks remain unknown, it is speculated that some may be present in bacteria.

Complexity and Potential Implications

1. Enzyme Instructions:
   • Some Obelisks contained instructions for enzymes needed for replication, indicating a higher complexity compared to previously described viroids.
   • However, they still lacked instructions for a protective outer shell.
2. Impact on Human Health:
   • The influence of Obelisks on human health remains unknown.
   • Viroids infecting bacteria may shape the human microbiome.
3. Evolutionary Debate:
   • Ongoing discussions about whether viruses evolved from viroids or if viroids evolved from viruses could be fueled by this new discovery.

Multiple Choice Questions (MCQs):

1. What are Obelisks?
   • a. Bacterial cells
   • b. Plant viruses
   • c. A class of viroids
   • d. Human genes
   • Answer: c. A class of viroids
2. Which bacterium is confirmed as a host for Obelisks?
   • a. Escherichia coli
   • b. Streptococcus sanguinis
   • c. Bacillus subtilis
   • d. Lactobacillus acidophilus
   • Answer: b. Streptococcus sanguinis
3. What distinguishes viroids from larger RNA-based viruses?
   • a. Viroids have a protective outer shell.
   • b. Viroids carry instructions for protein synthesis.
   • c. Viroids lack genetic material.
   • d. Viroids co-opt enzymes from their hosts.
   • Answer: d. Viroids co-opt enzymes from their hosts
4. Where were Obelisks found in the human body?
   • a. Heart and lungs
   • b. Liver and kidneys
   • c. Gut and mouth
   • d. Brain and spinal cord
   • Answer: c. Gut and mouth
5. What is the predicted 3D structure of Obelisks?
   • a. Spherical
   • b. Cuboidal
   • c. Tubular
   • d. Thin rod
   • Answer: d. Thin rod