SYDNEY, April 4 (Xinhua) -- A research team constructed a detailed evolutionary timeline of bacteria, revealing that some microbes used oxygen long before photosynthesis evolved, according to the University of Queensland (UQ) on Friday.

The study focused on how microorganisms responded to the Great Oxygenation Event (GOE) 2.33 billion years ago, a pivotal shift that transformed Earth's atmosphere to one that allows humans to breathe, said a UQ statement.

Dating bacterial evolution had been challenging due to incomplete fossil evidence, said Professor Phil Hugenholtz from UQ's School of Chemistry and Molecular Biosciences.

Most microbes left no direct fossil record, but ancient rocks contained chemical traces of bacterial activity, Hugenholtz said, adding by integrating geological and genomic data, scientists refined the evolutionary timeline, using the GOE as a time boundary.

The team used machine learning to analyze ancestral bacterial genomes, predicting whether they used oxygen. They also incorporated genetic data from mitochondria and chloroplasts, linked to early complex cells, to improve dating accuracy, said researchers from the University of Bristol, Queensland University of Technology, and UQ.

Findings published on Friday in Science indicated that at least three aerobic bacterial lineages emerged nearly 900 million years before the GOE. The earliest transition to oxygen use likely occurred 3.2 billion years ago in cyanobacterial ancestors, suggesting aerobic metabolism predates oxygenic photosynthesis.

Lead author Adrian Arellano Davin highlighted the broader potential of machine learning in evolutionary biology, saying this approach not only helped reconstruct ancient metabolisms but could also predict modern bacterial traits, like antibiotic resistance. Enditem

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