Ancient 'Asgard' Microbes May Have Harnessed Oxygen Long Before It Was Plentiful, Offering Clues to Complex Life's Origins

United States - Ekhbary News Agency

Revolutionary Discovery Rewrites Evolutionary History: Ancient 'Asgard' Microbes Likely Utilized Oxygen Early On

In a scientific revelation that could fundamentally alter our understanding of life's origins on Earth, a recent study indicates that a group of ancient microbes, scientifically termed 'Asgard archaea,' which are the closest known microbial relatives to plants and animals, may have developed the capability to use oxygen and derive energy from it millions of years before this gas became widespread in Earth's atmosphere. This finding, published in the journal 'Nature,' offers a novel perspective on one of biology's most profound mysteries: how the first complex cells, the progenitors of all complex life forms we recognize today, from towering trees to humans, came into existence.

For a long time, scientists presumed these ancient microorganisms favored oxygen-deprived environments. However, a new comprehensive genetic survey of ocean mud and seawater samples reveals a startling revelation: these organisms harbor the 'molecular machinery' that enables them to process oxygen and potentially convert it into energy. This discovery challenges previous assumptions and presents a plausible explanation for the pivotal symbiotic event between a simple microbe and a bacterium, which ultimately led to the formation of the first complex cells (eukaryotes).

Mitochondria, the powerhouses within complex cells, originate from bacteria that require oxygen for survival. Traditionally, it was believed that 'Archaea' (one of the three major domains of life) served as the host for these bacteria in the evolutionary narrative, and that many were adapted to survive in anaerobic (oxygen-free) conditions. The new study, however, posits that the Asgard archaea, the likely host, might have been significantly more tolerant to oxygen than previously thought.

Dr. Brett Baker, an associate professor of marine science at the University of Texas at Austin and a co-author of the study, stated in a press release: "Most Asgard archaea alive today have been found in environments devoid of oxygen. But it turns out that the lineages most closely related to eukaryotes inhabit oxygen-rich locations, such as shallow coastal sediments and floating in the water column, and they possess numerous metabolic pathways that utilize oxygen. This strongly suggests that our common eukaryotic ancestor likely possessed these processes as well."

Asgard archaea, named after the realm of the gods in Norse mythology, were first identified in 2015 when researchers reconstructed their genomes from deep-sea sediment samples near the Loki’s Castle hydrothermal vent. This research led to the establishment of the Asgard superphylum, encompassing archaeal groups like Lokiarchaeota, Thorarchaeota, and Odinarchaeota. Subsequent studies have indicated that these archaea carry multiple 'eukaryotic signature' genes, pointing to a close ancestral link with eukaryotes – organisms characterized by cells containing a nucleus and membrane-bound organelles.

To investigate how Asgard archaea might have tolerated oxygen, the research team focused their search on the Bohai Sea and the Guaymas Basin, environments known to support thriving microbial communities. They meticulously analyzed approximately 15 terabytes of environmental DNA extracted from marine sediments, successfully reconstructing over 13,000 microbial genomes and isolating hundreds of Asgard-specific genetic sequences.

Dr. Kathryn Appler, a postdoctoral researcher at the Institut Pasteur in Paris and a co-author of the study, commented: "These Asgard archaea are often overlooked in low-coverage sequencing efforts. However, the extensive sequencing endeavor and the integration of various sequencing and structural methodologies allowed us to discern patterns that were previously invisible prior to this genomic expansion."

Among these identified patterns were genes associated with aerobic respiration – the oxygen-dependent process that many organisms employ to efficiently extract additional energy from nutrients. Furthermore, the team utilized an artificial intelligence tool, AlphaFold2, to predict protein structures, thereby bolstering their evidence for the presence of oxygen-tolerant molecular machinery within these ancient microbes.

Notably, a specific branch of the Asgard archaea, known as Heimdallarchaeia (named after the watchman of the Norse gods), emerged as particularly significant. The researchers reported that numerous Heimdallarchaeia genomes contain components of the molecular systems responsible for electron transport and energy generation using oxygen, alongside enzymes that aid in managing toxic oxygen byproducts. If these oxygen-handling capabilities were indeed present in the archaeal ancestor of complex cells, it significantly simplifies the narrative of the crucial symbiotic merger.

Dr. Baker concluded: "Oxygen became available in the environment, and the Asgard archaea adapted to it. They discovered an energetic advantage in utilizing oxygen, which then paved the way for their evolution into eukaryotes." These findings not only illuminate the origins of complex life but may also open new avenues for understanding microbial evolution and their remarkable adaptability to changing environmental conditions.

Ekhbary News Agency Link