Since the 1960s, many scientists have argued that the emergence of eukaryotes — cells containing a clearly defined nucleus — happened in response to the oxygenation of Earths surface environment. However, new research from Stanford University and University of Exeter suggests that eukaryotes emerged in an anoxic environment in oceans.
Asgard archaeon. Scale bar – 500 nm. Image credit: Imachi et al., doi: 10.1038/s41586-019-1916-6.
We can now independently date eukaryogenesisDr. Daniel Mills is the lead author of the study. He is a researcher at Stanford University’s Department of Geological Sciences and at Portland State University’s Department of Biology.
Based on fossil and biological evidence, the timing of Eukaryogenesis is not related to these oxygen transitions in either the atmosphere (2.22 Billion years ago) or deep ocean (0.55 billion years ago).
Instead, mitochondria-bearing Eukaryotes are consistently dated between these two oxygenation events during an interval of deep-sea oxygenation and variable surface-water oxygenation.
The emergence of mitochondria — the energy-producing powerhouses of eukaryote cells — is now thought to be the defining step in eukaryogenesis.
The DNA of mitochondria differs from that of the cells in their environment. The new study examines the origin of this symbiotic relationship, which was famously advocated by Lynn Margulis (then Lynn Sgan) in 1967.
Dr. Mills stated that the 2015 discovery of Asgard archaea is a major clue.
Mitochondria-bearing Eukaryotes probably resulted in a merger of archaea, bacteria, and the DNA found in modern Asgard archaea is closer to the DNA found today in eukaryote Nuclei than to other archaea.
This is further evidence that the archaeon was the host that took in bacterium.
Asgard archaea live in anoxic ocean sediments, and they can live symbiotically with bacteria — possibly the same situation that led to the metabolic coupling that created the first eukaryote cells.
The new evidence supports the hydrogen hypothesis — that mitochondria were acquired in anoxic conditions — first put forward in 1998 by Bill Martin and Miklos Mller, said senior author Professor Tim Lenton, director of the Global Systems Institute at the University of Exeter.
The notion that oxygen was the catalyst for eukaryogenesis is a well-known fact.
Actually, mitochondrial aerobic respiratory system probably evolved later, becoming more widespread only in the last billion year as atmospheric oxygen increased to modern levels.
Our review was meant to bridge the gap between biology and geology, as connections were still waiting to be made after breakthroughs in both fields.
The teams PaperPublished in the journal Nature Ecology & Evolution.
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D.B. Mills et al. Eukaryogenesis, oxygen in Earth history. Nat Ecol Evol, published online April 21, 2022; doi: 10.1038/s41559-022-01733-y
