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

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