A newly identified microbe living within ancient stromatolite communities may offer insights into how complex life first emerged. Researchers captured the first direct images of an Asgard archaeon physically connected to a bacterium. The two microbes appear to exchange nutrients and other compounds. Scientists believe similar partnerships billions of years ago may have led to the first complex cells.
Stromatolites are layered communities built by microbes. They helped release early oxygen into Earth's atmosphere billions of years ago. A study published in *Current Biology* suggests these formations may also hold clues to the emergence of complex life. Associate Professor Brendan Burns, an evolutionary microbiologist at the University of New South Wales (UNSW) Sydney, co-led the research. The team discovered a previously unknown microbe in close association with another organism inside these “living fossils.” This project, with researchers from the University of Technology Sydney and The University of Melbourne, could help explain how simple cells began cooperating to form complex life.
The research team isolated a member of the Asgard archaea from samples collected in Shark Bay, Western Australia. Asgard archaea are believed to be closely related to the ancestors of eukaryotes. Eukaryotes are the cells that make up all plants and animals, including humans. A long-standing theory suggests that the first eukaryotic cell developed through an intimate partnership between an ancient archaeon and a bacterium. This relationship eventually produced mitochondria, the energy-producing structures in complex cells.
The new research provides the first visual evidence of an Asgard archaeon physically interacting with a bacterium. They are connected by extremely thin, tube-like structures called nanotubes. The archaeon also produces chains of budded vesicles and elaborate tube-like structures. The two microbes appear to complement each other chemically, producing compounds like vitamins, nutrients, and hydrogen that the other can use. This interaction could serve as a model for how such partnerships began and ultimately formed eukaryotes.
Growing the microbes in the laboratory proved challenging, taking four to five years. The researchers used electron cryotomography, a high-resolution three-dimensional (3D) imaging method, to visualize the interaction. Deep learning, a type of machine learning, was also used to predict protein structures in these microbes. This allows scientists to see ancient versions of cellular machinery central to complex life. The newly identified archaeon has been named *Nerearchaeum marumarumayae*, combining a reference to the Greek sea god Nereus with the Malgana word *marumarumayae*, meaning “ancient home.”
Stromatolites and microbial mats still form today in Shark Bay, a World Heritage-listed site. This site offers an opportunity to study conditions that may resemble early Earth. The findings highlight the importance of cooperation between organisms for survival. Researchers hope to identify additional microbial partnerships to further understand the evolution of complex life.
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