Complex Cells' Origins Have Been Started Without Oxygen

Complex Cells' Origins Have Been Started Without Oxygen ...

According to new research, the origin of complex cells was started without oxygen.

Many experts have argumented that the formation of eukaryotes (cells containing a clearly defined nucleus) occurred in response to Earth''s surface environment''s oxygenation.

Recent advances in the Earth and life sciences, according to a study of Stanford and Exeter, have jeopardized the subject.

These findings "decouple" the emergence of eukaryotes (also known as eukaryogenesis) from increasing oxygen levels, suggesting that eukaryotes in fact emerged in an anoxic (no-oxygen) environment in the ocean.

"We may now independently date eukaryogenesis and important oxygenation changes in Earth history," says Dr Daniel Mills of Stanford University.

"Based on fossil and biological records, the timing of eukaryogenesis does not correlate with these oxygen transitions in the atmosphere (2.22 billion years ago) or the deep ocean (0.5 billion years ago).

"Instead of these two oxygenation events, mitochondria-bearing eukaryotes are constant dated to between them, during an interval of deep-sea anoxia and variable surface-water oxygenation."

The development of mitochondria as the energy-producing "powerhouses" of eukaryote cells is now thought to be the driving force behind eukaryogenesis.

Mitochondria have different DNA than the cells in which they live, and the new paper investigates the potential origin of this symbiotic relationship, famously championed by biologist Lynn Margulis.

"The discovery of "Asgard" archaea (single-celled organisms) in 2015 offers a significant clue," Dr Mills said.

"Mitochondria-bearing eukaryotes are likely to be a result of a merger between archaea and bacteria, and the DNA in the modern Asgard archaea is more closely linked to the DNA found in the eukaryote nuclei today than it is to other archaea.

"This is additional evidence that the host who took the antibiotic was an archaeon."

Asgard Archaea live in anoxic ocean sediments, and they can symbiotically with bacteria, possibly the same situation that spawned the first eukaryote cells.

Professor Tim Lenton, Director of Exeter''s Global Systems Institute, said the new evidence supports the "hydrogen hypothesis" (that mitochondria were acquired in anoxic conditions) developed first in 1998 by Bill Martin and Miklos Muller.

"The assumption that oxygen would lead to eukaryogenesis has been taken for granted," he said.

"In fact, mitochondrial aerobic respiration has probably begun later, which has only become globally widespread in the last billion years as atmospheric oxygen reached new levels."

Following advances in both disciplines, Dr Mills said the review was intended to "celerate a gap" between biology and geology.

"In Earth history, eukaryogenesis and oxygen," a paper published in the journalNature Ecology & Evolution.

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