Calcium (Ca²⁺) is one of the most important second messengers, and is known to regulate metabolic and/or differentiation processes in eukaryotic cells. Much less is known about the role of Ca²⁺ in prokaryotes and especially cyanobacteria and how they sense Ca²⁺. Therefore, we aim to uncover the role of Ca²⁺ signaling in the multicellular lifestyle of the diazotrophic cyanobacteria. Recently within the frame of an international cooperation, we identified a novel Ca²⁺-Sensor protein (CSE protein). CSE protein is important for filament integrity, cell differentiation into heterocyst cells, N₂ fixation and the regulation of photosynthesis in diazotrophic multicellular cyanobacteria.

In addition, we are currently investigating the signaling roles of the cyclic di-nucleotides c-di-AMP and c-di-GMP in unicellular cyanobacteria. We identified several of novel c-di-AMP and c-di-GMP receptors as well as RNA-riboswitches, with putative roles in Carbon/Nitrogen metabolisms and photosynthetic day/night and/or phototaxis motility lifestyles. We are currently exploring the regulatory functions of those new c-di-AMP and c-di-GMP receptors.