Is Far-Red Light Photoacclimation (FaRLiP) activated in cyanobacteria exposed to M-dwarf starlight simulated spectra?

Rocky terrestrial exoplanets in the Habitable Zone of M-dwarf stars are ideal to potentially harbour life. However, such stars have different spectral characteristics respect to stars like our Sun, with almost no visible light available and major components in the far-red and infrared. This doesn’t seem suitable for oxygenic photosynthetic organisms, that evolved on Earth to absorb only VIS light. Thanks to the newly developed Star Light Simulator, an instrument able to simulate the emission spectra of different kinds of stars (Sun and M-dwarfs included), we were able to perform growth and photosynthetic analyses on a few species of cyanobacteria irradiated with M-dwarf simulated lights. We selected two strains of cyanobacteria, Chlorogloeopsis fritschii PCC6912 and Synechocystis sp. PCC6803. The first can perform the so-called Far-Red Light Photoacclimation (FaRLiP), that allows it to survive and evolve oxygen in environments rich in far-red lights, thanks to the production of peculiar chlorophylls (chl d and f) and far-red absorbing forms of phycobiliproteins. This makes it a perfect candidate to test the possibility of oxygenic photosynthesis in exoplanets irradiated by M-dwarf spectra. The second cyanobacterium is a model organism for photosynthetic research and was used as a control unable to perform such acclimation. We compared the growth and photosynthetic performances of the cyanobacteria exposed to the M-dwarf simulated light spectra. The results were compared with those obtained from the cyanobacteria exposed to a solar simulated light and a far-red light (730 nm LED). The possibility of oxygenic photosynthesis in exoplanets orbiting the habitable zone of M-dwarfs as well as the activation of the FaRLiP response under these simulated spectra is discussed.