Molecular investigation of the high radiation resistance of edible cyanobacterium Arthrospira sp PCC 8005

Arthrospira is an edible cyanobacterium used in the food supplement “Spirulina”. The aim of this work was to characterise its response to ionising radiation. Live cells of Arthrospira sp. PCC 8005 were irradiated with 60Co gamma rays. Arthrospira sp. PCC 8005 recovered and resumed photosynthetic proliferation after exposure to a dose of even 6400 Gy, which is a dose about 1000x higher than the lethal dose for most plant, animal and human cells. Biochemical, proteomic and transcriptomic analysis after irradiation with 3200 or 5000 Gy showed a strong reduction in photosynthesis activity and reduced pigment content. Irradiated cells showed reduced transcription for carbon fixation, and for pigment, lipid and secondary metabolite synthesis; while induced transcription of thiol-based antioxidant systems, photosensing and signalling pathways. Cells irradiated with 3200 or 5000 Gy did not show clear dsDNA damage, but transcriptomics did show significant activation of ssDNA repair systems and mobile genetic elements at RNA-level. Irradiated cells also expressed a group of conserved proteins of which the function in radiation resistance remains to be elucidated. This study revealed for the first time the high radiation resistance of Arthrospira, and the molecular systems involved, paving the way for its further exploitation for radiation protection. Arthrospira was exposed to two different doses of irradiation, 3200Gy and 5000Gy. Each of those irradiated experiment was performed in biological triplicate. For each of both conditions, a separate control (reference) was run in triplicate. This sums up to a total of 12 arrays.