Calibration and validation of an experimental setup to study by remote sensing cyanobacteria responses under exo-Earth simulated environments

In the last decade, using ground-based and space telescopes, more than 3900 new extrasolar planets have been discovered [1]. Among them, rocky Earth-like exoplanets orbiting the Habitable Zone (HZ) of M-type stars were found. M-type stars are particularly interesting for astrobiology, as they can live long enough to potentially sustain life evolution and are the most common type of stars in the Milky Way [2]. These stars, however, are quite different from our Sun: they are 10 times less luminous and have a different emission spectrum, with major components in the Far-Red and Infrared lights (FR-IR) and very low emission in the visible part of the light (VIS). The emission spectrum of the star is a fundamental constraint for oxygenic photosynthetic organisms while performing Oxygenic Photosynthesis (OP), as they mostly use VIS light to grow, with only few exceptions known [3, 4]. Speculations about photosynthetic organisms living in a planet orbiting around M-type stars have been made [5,6,7,8], but so far no one has performed growth experiment on terrestrial organisms using M-type star lights. To this aim in Padova (Italy) we started a collaboration between INAF (Astrophysics National Institute), CNR-IFN (Nanotechnologies and Photonics Institute) and BioPD (Department of Biology of the University of Padova). Through this agreement, a Star Light Simulator (SLS) and an Atmosphere Simulator Chamber (ASC) have been built. Using these newly designed devices, we study OP microorganisms such as cyanobacteria under simulated environmental conditions of terrestrial-like exoplanets orbiting M-type stars, to understand if they could maintain their oxygenic photosynthetic activity and furthermore impact on primeval atmospheres lacking oxygen [9]. Testing these conditions requires to set light spectra, temperature, pressure and atmospheric composition parameters that can be extremely different from terrestrial ones and imposes us to seal the ASC and assess the physiological responses of the cultures only at the beginning and at the end of the experiments. To overcome this issue, here we present a novel experimental setup to follow by remote sensing the growth and photosynthetic activity of oxygenic photosynthetic microorganisms by means of reflectivity, spectroscopic and fluorescence measurements, respectively. [1] https://exoplanets.nasa.gov/ [2] N.Y. Kiang, A. Segura, G. Tinetti, Govindjee, R.E. Blankenship, M. Cohen, J. Siefert, D. Crisp and V.S. Meadows, Astrobiology, 7, 1 (2007) [3] H. Miyashita, H. Ikemoto, N. Kurano, K. Adachi, M. Chihara & S. Miyachi, Nature, 383, 402 (1996) [4] F. Gan, S. Zhang, N.C. Rockwell, S.S. Martin, J.C. Lagarias, D.A. Bryant, Science, 345(6202), 1312-7 (2014) [5] J. Gale and A. Wandel, International Journal of Astrobiology, 16 (1), 1–9 (2017) [6] R.J. Ritchie, A.W.D. Larkum and I. Ribas, International Journal of Astrobiology, 17, 147-176 (2018) [7] K. Takizawa, J. Minagawa, M. Tamura, N. Kusakabe And N. Narita, Scientific Reports, 7, (2017) [8] A. Wandel, The Astrophysical Journal, 856, (2018) [9] Claudi, R.; Erculiani, M. S.; Galletta, G.; Billi, D.; Pace, E.; Schierano, D.; Giro, E.; D'Alessandro, M., IJAsB, 15, 35, (2016)