Topic: Biology

Scientists at The University of Texas at Austin discovered that some microbes called Asgard archaea can tolerate or even use oxygen. This finding supports the theory that complex life evolved in an environment with oxygen.

Scientists have long wondered how two very different microbes formed a close partnership, eventually giving rise to plants, animals, and fungi. One key question was: How did these two organisms meet if one required oxygen to survive while the other thrived only in oxygen-free environments? Researchers at The University of Texas at Austin now report evidence that may resolve this puzzle.

The team focused on a group of microbes called Asgard archaea, which are considered close relatives of the ancestors of complex life. Although most known Asgards live in deep-sea or other oxygen-poor environments, the new study shows that some members of this group can tolerate or even use oxygen.

This discovery strengthens the long-standing theory that complex life evolved as predicted, likely in an environment where oxygen was present. According to Brett Baker, an associate professor at UT, 'Most Asgards alive today have been found in environments without oxygen. But it turns out that the ones most closely related to eukaryotes live in places with oxygen, such as shallow coastal sediments and floating in the water column, and they have a lot of metabolic pathways that use oxygen.'

The Great Oxidation Event and Early Eukaryotes

Baker's team studies the genomes of Asgard archaea to identify new branches of the group and better understand how these microbes generate energy. Their latest findings align with what geologists and paleontologists have reconstructed about Earth's early atmosphere.

More than 1.7 billion years ago, oxygen levels in the atmosphere were extremely low. Then oxygen concentrations rose sharply during what scientists call the Great Oxidation Event, eventually approaching levels similar to those today. Within a few hundred thousand years of this dramatic increase, the earliest known microfossils of eukaryotes appear in the fossil record.

This close timing suggests that oxygen may have played a crucial role in the emergence of complex life. 'The fact that some of the Asgards, which are our ancestors, were able to use oxygen fits in with this very well,' Baker said. 'Oxygen appeared in the environment, and Asgards adapted to that. They found an energetic advantage to using oxygen, and then they evolved into eukaryotes.'

Symbiosis and the Birth of Mitochondria

The prevailing model holds that eukaryotes arose when an Asgard archaeon formed a symbiotic relationship with an alphaproteobacterium. Over time, the two organisms became integrated into a single cell.

Massive Genome Sequencing Effort

The work began with Appler's Ph.D. research at The University of Texas Marine Science Institute in 2019, when she extracted DNA from marine sediments. The UT team and collaborators ultimately assembled more than 13,000 new microbial genomes.

Why It Matters

This discovery helps us understand how complex life evolved on Earth. It also shows that scientists can learn about ancient environments by studying the microbes that live in them today.

Key Facts

• Scientists discovered that some Asgard archaea can tolerate or even use oxygen.
• These microbes are considered close relatives of the ancestors of complex life.
• The discovery supports the theory that complex life evolved in an environment with oxygen.
• Oxygen levels in the atmosphere rose sharply during the Great Oxidation Event, eventually approaching levels similar to those today.
• The earliest known microfossils of eukaryotes appear in the fossil record within a few hundred thousand years of this dramatic increase.

Key Terms

Asgard archaea

A group of microbes that are considered close relatives of the ancestors of complex life

Implications

This discovery helps us understand how complex life evolved on Earth. It also shows that scientists can learn about ancient environments by studying the microbes that live in them today.