Studying photosynthesis under Far-Red light and simulated M-dwarf star light: new experimental tools and suitable eukaryotic organisms with different positions in the tree of life

Several recently discovered Earth-like exoplanets are orbiting the Habitable Zone of M-dwarf stars. These are the most abundant and long-lived stars known in the Milky Way, making them ideal to potentially harbour life. However, such stars have different spectral characteristics respect to the Sun. They are less luminous and generate a light spectrum with far-red and infrared as major components, while emitting at very low level in the visible. These characteristics do not seem suitable for most oxygenic photosynthetic organisms we know from Earth, that evolved to absorb only visible light. Many researchers discussed the possibility of oxygenic photosynthesis in these worlds so far, but no experimental research has been done testing organisms under simulated M-dwarf spectra. At the university of Padova, a collaboration between the Department of Biology, the Astronomical Observatory (INAF) and the Institute of Photonics and Nanotechnology (IFN-CNR) led to the construction and the development of a new experimental tool. The setup is composed by three main parts: 1) a Star Light Simulator, able to generate different light intensities and spectra, including those of nonsolar stars; 2) an Atmosphere Simulator Chamber where cultures of photosynthetic microorganisms can be exposed to different gas compositions; 3) a reflectivity detection system to measure from remote the Normalized Difference Vegetation Indexes (NDVI). Such a setup allows us to monitor photosynthetic microorganism’s growth and gas exchange performances under selected conditions of light quality and intensity, temperature, and atmospheres simulating non-terrestrial environments. All parameters are detected by remote sensing techniques, thus without interfering with the experiments and altering the environmental conditions set. We initially focused on cyanobacteria as target microorganisms, due to their extraordinary capacities to withstand every kind of environment on the Earth as well as their ability to acclimate to Far-Red light. We are now selecting suitable eukaryotic photosynthetic organisms by testing at first their ability to acclimate to Far-Red light. The possibility of photosynthesis for prokaryotic and eukaryotic photosynthetic organisms under M-dwarfs light will be discussed.