Ancient Microbes May Have Used Oxygen Billions of Years Before Complex Life Evolved

More than 2 billion years ago, long before Earth’s atmosphere contained significant oxygen, a group of microbes may have already developed the ability to thrive in its presence, potentially laying the groundwork for the evolution of complex life as we know it.

Uncovering Ancient Adaptations

A new genetic survey of ocean mud and seawater has revealed evidence suggesting that Asgard archaea – the closest known microbial relatives of plants and animals – possess the molecular tools to manage oxygen, and possibly even harness it for energy production. Previously, many studied Asgards were found in oxygen-poor environments, creating a puzzle for scientists studying the origins of complex life.

Did You Know? Asgard archaea were first discovered in 2015 near the Loki’s Castle hydrothermal vent, leading to the creation of an Asgard superphylum including groups like Lokiarchaeota, Thorarchaeota, and Odinarchaeota.

The emergence of oxygen on Earth presented a challenge and an opportunity for early life. Mitochondria, the powerhouses within complex cells, rely on oxygen to function. However, archaea – one of the three primary domains of life – were thought to have largely evolved without oxygen. This new research suggests that the archaeal ancestor of complex cells, the Asgard archaea, may have been more tolerant of oxygen than previously believed.

The Role of Heimdallarchaeia

Researchers, led by study co-author Brett Baker, an associate professor of marine science at the University of Texas at Austin, found that Asgards closely related to eukaryotes often inhabit oxygen-rich environments like shallow coastal sediments. These Asgards exhibit metabolic pathways that utilize oxygen. This suggests that the ancestor of eukaryotes also possessed these oxygen-handling capabilities.

Expert Insight: The discovery of oxygen-handling capabilities in Asgard archaea resolves a key question in understanding the origins of complex life. If the archaeal host in the ancient microbe-bacterium merger was already adapted to oxygen, it makes the integration and eventual evolution of eukaryotes more plausible.

Specifically, a branch of Asgards known as Heimdallarchaeia stood out. Their genomes contain the molecular machinery for aerobic respiration, along with enzymes to manage the potentially harmful byproducts of oxygen metabolism.

What Might Come Next

If these findings are further substantiated, scientists may focus on understanding the specific mechanisms by which Asgard archaea tolerate and utilize oxygen. Further research could explore the evolutionary pressures that drove the development of these capabilities. It’s also possible that future studies will uncover additional Asgard groups with similar oxygen-handling traits, providing a more complete picture of early life’s adaptation to a changing atmosphere.

Frequently Asked Questions

What are Asgard archaea?

Asgard archaea are a group of microbes considered the closest known living relatives of plants and animals. They are part of a larger group of archaea discovered in deep-sea sediments.

When did this research take place?

The study was published on February 18 in the journal Nature.

What is the significance of oxygen in this research?

The research suggests that Asgard archaea may have been able to tolerate and even use oxygen long before it was abundant in Earth’s atmosphere, potentially explaining how the ancestor of complex life adapted to an oxygen-rich environment.

How might these findings change our understanding of the earliest forms of life on Earth?