• The article demonstrates that even the simplest filamentous cyanobacteria possess specialized structures that enable intercellular communication.
• This supports the hypothesis that the evolution of filaments contributed to the Great Oxidation of the Earth, as it played a key role in the proliferation of cyanobacteria.

Researchers from the CSIC at the Institute of Plant Biochemistry and Photosynthesis (IBVF)—a joint center of the Spanish National Research Council and the University of Seville—have carried out a study that delves into 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 are organized in long chains of interconnected cells. Unlike unicellular bacteria, this multicellular form allows them to distribute functions and better adapt to changing environments,” explains Enrique Flores, co-author of the article.

These cyanobacteria, present on Earth for 3,000 million years, were the first organisms to perform photosynthesis; that is, to use sunlight to produce energy and release oxygen as a byproduct. A process that, over millions of years, contributed decisively to transforming the primitive atmosphere of the Earth and making possible the emergence of more complex forms of life.

The article demonstrates that even the simplest filamentous cyanobacteria possess specialized structures that enable intercellular communication. This finding, together with the confirmation of the widespread presence of the genes responsible for these structures throughout the phylogenetic tree of cyanobacteria, makes it possible to deduce that cyanobacteria containing these genes arose even before the Great Oxidation. This supports the hypothesis that the evolution of filaments contributed to this event, as it was key for the proliferation of cyanobacteria.

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

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

The Great Oxidation of the Earth

Although the Earth formed around 4,500 million years ago, until about 2,400 million years ago the atmosphere lacked oxygen. From that point on, oxygen accumulated until reaching a level of approximately 1% of the current level. This 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, already in the Cambrian period (around 500 million years ago), that oxygen accumulated in the atmosphere to a level close to the current one, about 21%, allowing the development of animals, which base their metabolism on oxygen respiration.

Cyanobacteria are considered responsible for the initial accumulation of oxygen on Earth, as they are the organisms in which oxygenic photosynthesis evolved around 3,000 million years ago. They are the most morphologically diverse group of bacteria, ranging from unicellular organisms to filamentous ones, which are organized in chains of cells. The article now published demonstrates that the evolution of these filamentous forms may have been key to the proliferation of cyanobacteria, ultimately leading to the initial accumulation 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

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