Evolutionary Shift in Anabaena Cyanobacteria Repurposes Ancient DNA Machinery into a Structural Cytoskeleton

Scientists discover that Anabaena cyanobacteria repurposed an ancient DNA system into a cytoskeleton to control cell shape and support multicellularity.

By: AXL Media

Published: Apr 17, 2026, 7:38 AM EDT

Source: Information for this report was sourced from Institute of Science and Technology Austria

A Surprising Functional Pivot in Evolutionary History

Cyanobacteria have long been recognized as the biological architects of Earth's oxygen-rich atmosphere, facilitating the emergence of aerobic life approximately 2.5 billion years ago. While these organisms are traditionally studied for their photosynthetic capabilities, new research published in Science reveals a profound evolutionary repurposing of their internal machinery. A team led by Benjamin Springstein and Professor Martin Loose at the Institute of Science and Technology Austria (ISTA) found that a protein system previously dedicated to separating genetic material has been completely transformed. In the multicellular cyanobacterium Anabaena, this system no longer moves DNA but instead acts as a structural scaffold that dictates the physical shape of the cell.

From Mobile Plasmids to Chromosomal Scaffolding

The discovery began with a serendipitous observation regarding the ParMR system, a mechanism typically found on mobile genetic elements known as plasmids. In most bacteria, this system functions like a spindle to pull DNA apart during cell division. However, Springstein noted that in Anabaena, the system was encoded directly onto the main chromosome. Initial hypotheses suggested it might be responsible for segregating these essential chromosomes, but experimental data told a different story. The protein ParR was found to have lost its ability to bind to DNA entirely, opting instead to associate with the lipid membranes of the cell's inner wall.

Architectural Changes at the Molecular Level

To understand how the system shifted functions, the researchers utilized cryo-electron microscopy to view the protein filaments at near-atomic resolution. They discovered that the filaments in Anabaena are bipolar, meaning they have the capacity to grow and shrink from both ends simultaneously. This is a significant departure from the polar filaments found in DNA-segregation systems of other bacteria. Instead of forming bundles in the cytoplasm to move cargo, these proteins assemble into an array just beneath the inner cell membrane. This organization mimics a cell cortex, providing the tension and support necessary to maintain a specific cellular geometry.