Even ancient bacteria possessed intercellular communication structures like humans today, study finds

Communication between cells in plants, animals and humans takes place via specialized connecting structures. An international team led by biologists from Heinrich Heine University Düsseldorf (HHU) and involving the University of Tübingen has now discovered that the regulation of very similar structures was already present in multicellular bacteria, implying that it must have originated much earlier in the course of evolution. In their paper published in The EMBO Journal, the researchers describe how the exchange of calcium plays a central role in bacteria, just as it does in humans.

Higher eukaryotic cells—i.e., cells with a nucleus, such as those found in humans and all higher animals—possess structures that connect neighboring cells. It is known that, among other things, these structures facilitate fundamental communication processes between cells; without them, tissues such as the human heart could not function. Furthermore, nerve cells transmit the signals that control our bodies via these connecting structures. These structures and communication between cells are regulated through the exchange of calcium ions (Ca²⁺).

The research group from the Institute of Phototrophic Microbiology led by Junior Professor Dr. Khaled Selim has now discovered that similar communication processes and connecting structures in bacteria are also regulated by calcium signals. Bacteria, however, are simpler cells that lack a nucleus, so-called prokaryotes.

Selim said, “It came as a big surprise to us that one of the earliest life forms on Earth—evolutionarily older and simpler cells—had already developed communication structures regulated by calcium signals similar to those found in the cells of higher organisms, such as animals and humans.”

The research team reports the presence of such communication structures in multicellular cyanobacteria. “Analogous to the connecting structures in eukaryotes known as gap junctions—traditionally considered a eukaryotic trait—cyanobacteria coordinate their cell-to-cell communication via connecting structures called ‘septum junctions.’ The signals regulating this cell-to-cell communication and the formation of septum junctions were previously largely unknown,” said Teresa Müller, a doctoral researcher in Selim’s research group within the Cluster of Excellence “Controlling Microbes to Fight Infections” (CMFI) at the University of Tübingen and first author of the study.

The biologists in Düsseldorf discovered a calcium-binding protein (for short: CSE) found exclusively in multicellular cyanobacteria. Using nuclear magnetic resonance (NMR) spectroscopy, they determined the structure of CSE in its calcium-bound state and demonstrated that it functions as a calcium-buffering protein. Furthermore, using cryo-electron microscopy, the researchers observed that mutant bacterial cells lacking CSE exhibited significantly fewer connecting structures.

Selim emphasizes, “Our research offers new insights into evolution. It suggests that the functional principles of higher organisms were already present in simple, multicellular bacteria that form tissue-like structures, meaning that these cellular connections date back a billion years—before the time when the evolutionary lineages of eukaryotes and prokaryotes diverged.”

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