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Unraveling Bacterial Evolution: New Insights into Oxygen Use

Researchers from the University of Queensland, in collaboration with several international institutions, have made significant strides in understanding the timeline of bacterial evolution. Their findings indicate that certain bacteria may have utilized oxygen long before they developed the capability to produce it via photosynthesis.

This multinational effort, involving experts from the Okinawa Institute of Science and Technology, the University of Bristol, and Queensland University of Technology along with UQ, delves into the microbial responses triggered by the Great Oxygenation Event (GOE) that occurred approximately 2.33 billion years ago. This monumental shift transformed Earth’s atmosphere from an oxygen-poor environment to one that supports human life.

Professor Phil Hugenholtz of UQ’s School of Chemistry and Molecular Biosciences pointed out that establishing precise timelines for bacterial evolution around the GOE has been challenging due to the sparse fossil record available for microbial life.

“Most microorganisms do not leave behind a direct fossil trace, resulting in significant gaps in our understanding of life’s history on our planet,” he explained. “However, early rock formations contain chemical evidence that hints at the lifestyles and diets of these ancient bacteria. By simultaneously analyzing geological and genomic data, we were able to fill in some of these gaps.”

The research team employed the GOE as a chronological marker, hypothesizing that most aerobic bacterial branches would not predate this event, unless supported by fossil or genetic evidence. They began by estimating the genes present in the ancestors of these microorganisms and utilized machine learning to determine their possible oxygen utilization.

To enhance the efficacy of fossil data, the team incorporated genes from mitochondria, associated with alphaproteobacteria, and chloroplasts, linked to cyanobacteria. This approach allowed for a more accurate estimation of significant evolutionary events.

“Our results indicate that at least three lineages capable of aerobic respiration emerged nearly 900 million years prior to the GOE,” Professor Hugenholtz noted. “This suggests that the adaptation for oxygen use likely occurred well in advance of its substantial presence in the atmosphere.”

Further exploration revealed that the earliest known transition to aerobic metabolism may have originated around 3.2 billion years ago within the cyanobacterial lineage, implying the possibility of aerobic metabolism occurring prior to the emergence of oxygenic photosynthesis.

Dr. Adrián Arellano Davín, the lead author of the study, emphasized the innovative combination of genomic data, fossil evidence, and Earth’s geochemical history in their research. This multidisciplinary approach employed advanced technologies to refine the understanding of evolutionary timelines.

“Through machine learning to infer cell functions, we not only predict the aerobic processes of ancestral bacteria, but we can also utilize incomplete genomic information to forecast other traits that could be significant today, such as antibiotic resistance,” Dr. Davín stated.

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