Amazing stuff!
"Aerobic respiration—using oxygen to power the process of producing cellular fuel—was a huge development for life on Earth. After some microbes figured out photosynthesis, levels of oxygen in the atmosphere jumped dramatically, resulting in what’s commonly called the Great Oxygenation Event some 2.3 billion years ago, paving the way for oxygen-breathing life to take over. But it’s never been clear when the ability to metabolize oxygen evolved. Now, thanks to a combination of fossil, genetic, and geological data, researchers have a new estimate— and it’s 900 million years before photosynthesis pumped oxygen into the atmosphere.
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From the editor's summary and abstract:
"Editor’s summary
When exploring deep time, the problem is that there are few, if any, good fossils of the earliest living organisms, and it is impossible to precisely date the evolution of those that do exist.
One calibration point is provided by the impact event about 4.5 billion years ago that resulted in sterilization of Earth and formation of the Moon. Davín et al. used molecular clocks, machine learning, and phylogenetic reconciliation to present a reconstruction of the evolution of Earth’s bacterial biosphere over the past 4 billion years with particular emphasis on aerobic metabolisms. Their analysis showed that the last common ancestor of bacteria likely existed 4.4 to 3.9 billion years ago, and aerobic organisms likely emerged before the Great Oxidation Event (2.43 to 2.33 billion years ago). Oxygen tolerance may have been a prerequisite for, rather than a consequence of, the evolution of oxygenic photosynthesis. ...
Structured Abstract
INTRODUCTION
Microbial life dominates the biosphere, but a timescale of early microbial evolution has proven elusive as a result of an inadequate fossil record. The lack of maximum age calibrations—the earliest point in time at which a given group might have emerged—is particularly problematic.
However, the geochemical record bears the imprint of microbial metabolism through time, providing a complementary source of information.
A pivotal event in this history was the Great Oxidation Event (GOE) ~2.43 to 2.33 billion years ago (Ga), which marked a substantial increase in atmospheric oxygen.
This transition, driven by the evolution of cyanobacterial oxygenic photosynthesis and carbon burial, transformed the biosphere from predominantly anoxic to oxic, causing widespread adaptation to oxygen. In this study, we used the temporal link between atmospheric oxygenation and the evolutionary spread of aerobic metabolism to calibrate the phylogeny of the bacterial domain.
RATIONALE
To date the bacterial tree, we introduced multiple new maximum age calibrations by linking the GOE to the age of aerobic lineages. We used a Bayesian approach that assumes that aerobic nodes are unlikely to be older than the GOE but can predate it given sufficient evidence from fossils or sequence divergence. To implement this approach, we integrated phylogenetic reconciliation with machine learning to map transitions from anaerobic to aerobic lifestyles onto the bacterial tree. By aggregating signals across the genome, we could robustly infer aerobic and anaerobic phenotypes from incomplete ancestral gene repertoires.
RESULTS
We identified 84 anaerobic to aerobic transitions on a species tree of 1007 bacteria. Most transitions occurred after the GOE and were driven by horizontal acquisition of respiratory and oxygen tolerance genes.
However, despite the GOE calibration, at least three transitions predated this event, suggesting that aerobic respiration evolved before widespread atmospheric oxygenation and may have facilitated the evolution of oxygenic photosynthesis in cyanobacteria.
Our molecular clock analyses estimated that the last bacterial common ancestor lived in the Hadean or earliest Archaean era (4.4 to 3.9 Ga), whereas bacterial phyla originated in the Archaean and Proterozoic eras (2.5 to 1.8 Ga); most bacterial families are as old as land plants and animal phyla, dating back to the late Proterozoic (0.6 to 0.75 Ga).
CONCLUSION
We infer that the earliest aerobic bacteria emerged in the Archaean, predating the GOE by 900 million years. After the GOE, aerobic lineages experienced faster diversification than their anaerobic counterparts, highlighting the impact of atmospheric oxygenation on bacterial evolution. The approach developed here provides a framework for linking microbial traits to Earth’s geochemical history, offering a pathway for exploring the evolution of other phenotypes in the context of Earth’s history."
An integrated approach to date bacterial evolution and reconstruct the history of oxygen adaptation.
