Researchers from the IBVF provide new clues about the biological origin of the Earth Great Oxidation

Researchers from the Spanish National Research Council (CSIC) at the Institute of Plant Biochemistry and Photosynthesis (IBVF) — a joint center of the CSIC and the University of Seville — have conducted a study that explores the role of filamentous cyanobacteria in the accumulation of oxygen in the Earth’s atmosphere, a key phenomenon for the development of life as we know it today. The work is published in the journal Communications Biology.

“Filamentous cyanobacteria are very ancient microorganisms that organize themselves into long chains of interconnected cells. Unlike unicellular bacteria, this multicellular form allows them to distribute functions and adapt better to changing environments,” explains Enrique Flores, co-author of the article.

These cyanobacteria, present on Earth for about 3 billion years, were the first organisms to carry out photosynthesis—that is, to use sunlight to produce energy and release oxygen as a by-product. Over millions of years, this process contributed decisively to transforming the primitive atmosphere of the Earth and making the emergence of more complex life forms possible.

The article shows that even the simplest filamentous cyanobacteria possess specialized structures that enable cell-to-cell communication. This finding, together with confirmation of the widespread presence of the genes responsible for these structures across the cyanobacterial phylogenetic tree, suggests that cyanobacteria containing these genes appeared even before the Great Oxidation Event. This supports the hypothesis that the evolution of filaments contributed to this event, since it was key to the proliferation of cyanobacteria.

“Being fully multicellular organisms with complex physiology, they were able to proliferate and greatly contribute to the Great Oxidation of the Earth, allowing the development of more complex life forms,” concludes Mercedes Nieves, researcher at the IBVF and first author of the study.

In addition to the IBVF, the research involved the University of Bristol (United Kingdom) and Freie Universität Berlin (Germany).

The Great Oxidation of the Earth

Although the Earth formed about 4.5 billion years ago, the atmosphere lacked oxygen until around 2.4 billion years ago. From that point onward, oxygen accumulated until reaching approximately 1% of its current level. This event is known as the Great Oxidation of the Earth, a crucial phenomenon for the development of life as we know it today.

It was not until later, during the Cambrian period (around 500 million years ago), that atmospheric oxygen accumulated to a level close to the present 21%, enabling the development of animals, whose metabolism depends on oxygen-based respiration.

Cyanobacteria are considered responsible for the initial accumulation of oxygen on Earth, as they are the organisms in which oxygenic photosynthesis evolved about 3 billion years ago. They are the most morphologically diverse group of bacteria, ranging from unicellular organisms to filamentous forms organized into chains of cells. The newly published article demonstrates that the evolution of these filamentous forms may have been key to the proliferation of cyanobacteria, ultimately leading to the initial buildup of oxygen in the atmosphere.

Reference: Boden JS, Nieves-Morión M, Nürnberg D, Arévalo S, Flores E, Sánchez-Baracaldo P. (2025) Evolution of multicellularity genes in Cyanobacteria in the lead up to the great oxidation event. Communications Biology. DOI: 10.1038/s42003-025-09247-6