Microbe Duo May Explain the Origin of Complex Life on Earth

Scientists have identified a symbiotic relationship between two ancient microorganisms that may have played a crucial role in the emergence of complex life on Earth. The discovery, reported by Futura and based on research published in the journal Nature Microbiology, centers on a bacterium and an archaeon found living in close association in the hypersaline waters of Shark Bay, Western Australia. This partnership offers a compelling model for how early eukaryotic cells — the foundation of all complex life — might have originated through cooperative interactions between prokaryotes.

The research team, led by scientists from the French National Centre for Scientific Research (CNRS) and Sorbonne University, observed that the bacterium, a member of the Desulfobacterota phylum, metabolizes sulfur compounds and produces organic acids as byproducts. The archaeon, classified within the Asgard archaea superphylum, consumes these acids and in return provides the bacterium with essential nutrients and a stable micro-environment. This mutual exchange creates a tightly coupled metabolic loop that enhances the survival of both partners in an otherwise extreme habitat.

What we’re seeing is not just coexistence, but a genuine metabolic interdependence where each organism relies on the other’s waste products to thrive. This kind of interaction is exactly what we would expect in the early stages of eukaryogenesis, where an archaeal host began to internalize a bacterial partner.

Dr. Mélanie Leclerc, CNRS Microbial Evolution Laboratory

Asgard archaea have gained significant attention in evolutionary biology since their discovery in deep-sea sediments in 2015. Genetic analyses show they possess numerous eukaryotic-like genes, particularly those involved in membrane trafficking and cytoskeletal dynamics — features absent in typical bacteria and archaea but essential for complex cellular organization. The new findings from Shark Bay suggest that these genetic traits may have been refined not in isolation, but through sustained metabolic cooperation with bacterial partners.

The hypersaline environment of Shark Bay, home to living stromatolites formed by microbial mats, serves as a modern analog for the conditions that may have prevailed on early Earth. In such settings, where oxygen is scarce and chemical gradients are steep, metabolic handoffs between microbes could have provided selective advantages driving increased complexity. Over time, such partnerships may have led to the stable internalization of one partner by the other — a process widely hypothesized as the origin of the mitochondrion and, by extension, the eukaryotic cell.

To confirm the nature of the interaction, researchers used metagenomic sequencing, fluorescence in situ hybridization (FISH), and nano-scale secondary ion mass spectrometry (NanoSIMS) to map the spatial arrangement and metabolic exchange between the two organisms. The imaging revealed consistent physical proximity, with the archaeon frequently surrounding the bacterium, suggesting a stable, long-term association rather than transient contact.

While the discovery does not prove that this exact partnership led to eukaryogenesis, it provides a tangible, observable model of how such a transition could begin. The researchers emphasize that similar consortia may exist in other extreme environments — such as hydrothermal vents or anaerobic sediments — and warrant further investigation as potential analogs for early eukaryotic precursors.

Insights from this study also have implications beyond origins-of-life research. Understanding how microbes establish and maintain metabolic dependencies can inform synthetic biology efforts to engineer stable microbial consortia for industrial applications, including biofuel production, carbon capture, and bioremediation. The principles of cross-feeding and environmental adaptation observed here may help scientists interpret data from Mars missions seeking signs of ancient or extant microbial life.

The research underscores the importance of studying microbial interactions in natural ecosystems, particularly in environments that resemble early Earth. As Shark Bay continues to yield insights into some of the planet’s oldest living systems, scientists are advocating for increased protection of such sites, which serve as both evolutionary laboratories and archives of life’s deep history.