The Discovery of Obelisks: A New Class of Biological Entities Challenging the Taxonomy of Life

The Discovery of Obelisks: A New Class of Biological Entities Challenging the Taxonomy of Life. A recent study published in the journal Cell in 2024 has revealed the existence of a new class of biological entities called 'obelisks.' These entities are round RNA molecules smaller than viruses and were found in the human mouth and gut microbiome. Obelisks encode previously unknown proteins, challenging the boundaries between living and non-living things. This discovery has the potential to change our understanding of the root of life and may have implications for human health.. Introduction: Blurring the Lines of Life For centuries, scientists have been trying to define exactly what is meant by 'life.' Classical taxonomy divides the world into three domains: Bacteria, Archaea, and Eukarya. Viruses, although not considered fully alive, are often placed on the fringes of this definition. Now, a startling discovery has further blurred the line. An international team of researchers led by Dr. Ivan Zheludev from Stanford University has found a new class of biological entities called 'obelisks.' These entities are not viruses, not bacteria, and not any known form of cellular life. They are small, round RNA molecules, but they have the ability to encode proteins never seen before. Methodology: Hunting for Mysterious RNA in a Large Database The study published in Cell used advanced bioinformatics to analyze more than 5.4 million sets of metagenomic data collected from various sources, including the Human Microbiome Project and other databases. They developed a special algorithm to search for unknown round RNA sequences. The result was the discovery of nearly 30,000 different types of obelisks, spread across samples from the human mouth and gut. Interestingly, obelisks were not detected in samples from other body parts, such as the skin or lungs, suggesting that they may have a special relationship with the gut microbiome. Unique Features of Obelisks: Smaller than Viruses, Stranger than Viroids Obelisks have several features that distinguish them from other biological entities. First, they are extremely small, with RNA lengths of around 1,000 nucleotides, much smaller than viruses, which typically range in the tens of thousands of nucleotides. Second, their structure is a round RNA, similar to viroids, but viroids do not encode proteins. Obelisks, on the other hand, encode one or two proteins called 'obulins.' The obulin proteins have no similarity to any known proteins in the database, suggesting that they may have unique biological functions. Third, obelisks lack a protein coat or capsid like viruses and cannot replicate independently. Instead, they depend on a specific host bacterium in the microbiome to replicate. Implications for Taxonomy and the Definition of Life The discovery of obelisks challenges the existing biological taxonomy. If viruses are considered the most minimalist form of 'living' things, obelisks are even more minimalist. They exist on the boundary between complex genetic molecules and living organisms. Researchers are hesitant to call them 'forms of life' because they lack their own metabolism. However, their ability to encode proteins and depend on a host for replication makes them difficult to classify. Dr. Zheludev stated in an interview with Nature News that 'obelisks may represent an evolutionary transition between short RNA molecules and real viruses.' This raises new questions about the origin of life and how the first virus may have emerged. Impact on Human Health: Are Obelisks Pathogens or Commensals? So far, there is no direct evidence that obelisks cause disease in humans. However, their widespread presence in the mouth and gut microbiome raises questions about their role in human health. Initial studies found that obelisks are more common in individuals with periodontal disease than in healthy individuals. This may suggest that obelisks can serve as biological markers for certain diseases or that they may play a role in disease pathogenesis. Researchers are now actively investigating the interactions between obelisks and host bacteria, as well as their potential impact on the human immune system. Challenges and Future Research Directions Although the discovery of obelisks is a significant achievement, much remains unknown. One of the main challenges is culturing obelisks in the laboratory. Because they depend on specific host bacteria, researchers need to identify these hosts first. Additionally, the function of obulin proteins remains a mystery. Do they help obelisks replicate, or do they manipulate host cells for their own purposes? Further research using cryo-electron microscopy and molecular biology techniques is needed to answer these questions. The research team also plans to search for obelisks in the microbiomes of other animals, including livestock and wildlife, to understand their evolutionary distribution. Conclusion: A New Era in Microbiology The discovery of obelisks opens a new page in the field of microbiology and evolutionary biology. It reminds us that the microbial world is full of surprises, and that the definition of life may need to be re-examined. With advances in sequencing technology and bioinformatics, we may discover more enigmatic entities like obelisks in the future. For the general public, this discovery highlights the complexity of the ecosystem within our own bodies. Although obelisks may not directly affect our daily lives, a deeper understanding of the human microbiome could lead to new therapies for chronic diseases like inflammatory bowel disease and obesity. Science continues to surprise us, and obelisks are proof that the biological universe still holds many secrets waiting to be uncovered.