Abstract EANA2025-136

Understanding the resistance of cyanobacteria to ionizing radiation is of significant interest in astrobiology, both for their potential role in life-support systems during space missions and for investigating the origins of photosynthetic life on Earth. In most living organisms the exposure to ionizing radiation—including Ultraviolet C radiation (UVC), gamma rays, X-rays, and neutron radiation—has profound effects on biochemical and physiological functions, directly interacting with biomolecules, but also indirectly damaging them through the induction of strong oxidative stress.  Nevertheless, some cyanobacterial species preserved to this day some primeval characteristics, evolved on the inhospitable surface of the Archean Earth, demonstrating to be highly resistant to ionizing radiation. They utilize specific mechanisms such as self-shading, production of protective compounds, and efficient repair of biomolecular damage during recovery phases [1]. 

While the tolerance of desiccated cyanobacterial cells to short-term high-dose ionizing radiation has already been extensively investigated [2], [3], the effects of chronic low-dose exposure on metabolically active cells remain largely unexplored. To fill this knowledge gap, in this work we tested the effect of prolonged permanence of biofilms under a simulated daily radiation dose of lunar surface on two species of cyanobacteria: Synechococcus sp. PCC7335 and Chlorogloeopsis fritschii PCC6912. These strains were selected for their ability to perform oxygenic photosynthesis using Far-Red light (730–750 nm) [4], [5]: the most ancestral photosynthetic mechanism still in existence [6], [7] and key characteristic linked to the synthesis of ultraviolet radiation (UVR) protectant compounds [8].

Biofilms of the selected organisms acclimated to both a Solar simulated light spectrum (SOL) and a Far-Red monochromatic light (FR) were exposed to 1 mGy of Californium 252 (252Cf) neutrons over a period of six months, simulating for daily low-dose rate radiation of Moon environment [9]. These experiments were carried out in the simulation facility of the Colorado State University, Colorado, USA.

At the end of the exposure period, cell vitality tests and phenotype characterization were carried out. Pigment content and photosynthetic efficiency were also assessed. Moreover, in vivo spectroscopy and Raman microscopy analyses were performed. The recovery capacity of the cell cultures was then evaluated by inoculating the cells into liquid growth medium and comparing growth curves of control and irradiated samples.

All of the irradiated biofilms, regardless of their photosynthetic pre-acclimation, proved to be capable of resuming cell division rates comparable to the control samples. Overall, the results proved that chronic exposure to low doses of ionizing radiation seems not to affect the survival and the metabolic activity of the tested cyanobacteria.

 

 

[1]Mosca, C. et al. (2022). International Journal of Astrobiology, 21(5), 380-391.

[2]Verseux, C. et al. (2017). Astrobiology, 17(2), 118-125.

[3]Baqué, M. et al. (2020). Life, 10(6), 83.

[4]Battistuzzi, M. et al. (2023). Frontiers in Plant Science, 14, 1070359.

[5]Liistro, E. et al. (2024). Physiology and Biochemistry, 108793.

[6]Gisriel, C. J. et al. (2022). Microorganisms, 10(7), 1270.

[7]Antonaru, L. A. et al. (2025). Current Biology, 35(11), 2539-2553.

[8]Llewellyn, C. A.et al. (2020). Scientific Reports, 10(1), 20638.

[9]Takahashi, A. et al. (2020). Life, 10(11), 274.