Billions of years ago, simple microbes laid the groundwork for the sophisticated immune systems found in complex organisms like humans. Recent findings from the University of Texas (UT) reveal that without these microscopic pioneers, our ability to combat viruses might have been significantly diminished.
Originally, our planet was dominated by a diverse array of single-celled organisms, long before multicellular life came into existence. It was from these primordial life forms that complex life eventually emerged. In 2015, scientists discovered living descendants of these ancient microbes, known as a superphylum of archaea called Asgard, in ocean sediments between Greenland and Norway. By 2020, these Asgard archaea were cultivated in laboratories, marking a significant breakthrough in microbiology.
Under the microscope, Asgard archaea resemble bacteria, yet they share a closer evolutionary relationship with eukaryotic life forms, such as plants and animals. The genomes of these archaea suggest that they diverged from our eukaryotic ancestors roughly 2 billion years ago, sparking the evolution of all complex life on Earth.
The transition to complex organisms involved significant structural changes, including the development of a nucleus, potentially derived from a viral source which provided a protective enclosure known as a viral factory. Another critical development was the incorporation of mitochondria, likely acquired from engulfed bacterial predecessors.
Despite the ancient nature of these microbes, our understanding of their defence mechanisms against bacteria and viruses remains limited. However, UT researchers have employed artificial intelligence to analyze newly expanded Asgard genomes, uncovering ancient immune defences that have evolved over millennia.
One of the most striking discoveries is the identification of immune proteins similar to viperin, which are present in all complex life forms today and were likely inherited from the last common ancestor of archaea and eukaryotes. Viperin proteins combat viral infections by inhibiting viral replication, a vital defense mechanism shared across various life forms.
Moreover, the research highlights that nearly 8 percent of the defence genes in Asgard archaea are linked to argonautes, another set of immune proteins. Argonautes help prevent viral spread by slicing up viral DNA, acting as a programmable immune system across different life domains.
To further validate these findings, scientists cloned the genetic blueprints of viperin from Asgard archaea into E. coli bacteria. When exposed to viruses, the modified bacterial cells exhibited enhanced resistance, demonstrating the enduring impact of these ancient microbial defences.
This ongoing research not only highlights the evolutionary continuity from microbes to humans but also underscores the fundamental role of these ancient organisms in shaping our biological defences. Thanks to these microscopic forebears, our immune systems are equipped to tackle a plethora of viral threats, a testament to the enduring legacy of evolution.
The insights from this study were published in Nature Communications, offering a profound glimpse into our connection with the microbial world.
