New found ‘obelisks’ join viruses, viroids as third unusual life form
- February 28, 2024
- Posted by: OptimizeIAS Team
- Category: DPN Topics
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New found ‘obelisks’ join viruses, viroids as third unusual life form
Subject: Science and tech
Section: Biotech
Context:
- Scientists at Stanford University have identified a new, remarkably simple form of life, which they have named ‘obelisks,’ positioning it in complexity between viruses and viroids.
Details:
- This discovery emerged from analyzing genetic material from bacteria in the human gut, utilizing next-generation sequencing (NGS).
- NGS is a sophisticated method that enables the parallel sequencing of genomes from various organisms in fragments.
- The identification of obelisks adds another category to the entities existing on the boundary of life, joining viruses and viroids in the continuum of biological simplicity.
Virus and viroid:
- For nearly 70 years since their discovery in 1898, viruses, with their host dependence, parasitism, and small genomes, were considered the only entities on the border between life and non-life. Viruses are made of a nucleic acid core (DNA or RNA) surrounded by a protein coat, and sometimes a lipid layer, and replicate by infecting host cells and using their machinery to produce more viruses.
- This changed in 1971 when Theodor Diener, a plant pathologist at the U.S. Department of Agriculture’s Research Center, discovered an organism responsible for potato spindle tuber disease that was even simpler than viruses.
- This organism, which he named ‘viroids,’ consisted of naked RNA without the lipid layer or protein coat typical of viruses.
- Unlike viruses, viroid RNA doesn’t code for any proteins; it merely propagates itself.
- Viroids are significantly smaller than viruses, with 250-400 base pairs compared to the thousands in RNA viruses.
- Diener’s discovery of viroids added a new layer to our understanding of plant pathology and expanded the realm of entities existing at the edge of life, challenging the unique status of viruses in this regard.
NGS (next-generation sequencing) and circular genome:
- NGS is a method that sequences genome fragments in parallel.
- The researchers developed a software script to detect circular RNA genomes, indicative of viroid-like entities.
- Through this approach, they analyzed5.4 million RNA sequence datasets from human gut bacteria, identifying 29,959 distinct obelisks across 220,000 datasets.
- Further exploration showed obelisks also present in bacteria from the human mouth and across all seven continents, highlighting their widespread presence.
- Unlike viroids, which have small, circular RNA genomes that do not code for proteins, obelisks have larger RNA genomes of about a thousand base pairs that appear to code for two unique proteins, unlike any known proteins from other life forms.
- This significant discovery broadens our understanding of the complexity and diversity of life forms, especially those at the micro-scale, living within the human body.
A link to S. sanguini:
- The recent discovery of ‘obelisks,‘ a new form of life situated between viruses and viroids, faces a challenge in linking specific obelisks to their bacterial hosts due to the collective analysis of RNA data from gut or oral bacteria.
- However, by individually analyzing RNA from lab-grown bacteria, researchers successfully linked a particular obelisk to Streptococcus sanguini, a species common in the human mouth.
- This finding raises several questions about obelisks, including their replication process,transmission methods, potential pathogenicity to bacteria, evolutionary history, and possible impacts on human health and disease.
- Despite these uncertainties, the discovery highlights the blurring lines between life and non-life, emphasizing the complexity and diversity of life forms at the microscopic level.
Source: TH