A novel strain of radiotolerant microalga Bracteacoccus sp. employs a synergistic antioxidant defense system to mitigate gamma radiation-induced oxidative stress

چکیده مقاله

Purpose Ionizing radiation inflicts severe damage in biological systems primarily through oxidative stress. While some radioresistant prokaryotes are well-studied, the defense mechanisms in eukaryotic microalgae remain largely unexplored. This study aims to characterize the physiological and biochemical defense strategies of a novel radiotolerance strain of the eukaryotic microalga Bracteacoccus sp. against gamma radiation. Materials and methods Cultures in the exponential growth phase were exposed to gamma radiation doses ranging from 0 to 3200 Gy. Post-irradiation, growth kinetics, photosynthetic pigments, the ketocarotenoid astaxanthin, proline, total soluble protein, oxidative stress markers (malondialdehyde/MDA and hydrogen peroxide/H2O2), and the activities of key antioxidant enzymes (superoxide dismutase/SOD, catalase/CAT, ascorbate peroxidase/APX) were analyzed over a 37-day recovery period. Results The microalga exhibited high radiotolerance, surviving all tested doses. A dose-dependent growth delay was observed, with full recovery achieved by day 37. The calculated LD50 was 1160 Gy, substantially higher than most previously reported microalgae. The defense mechanism was characterized by a significant accumulation of total carotenoids and astaxanthin (up to 3-fold), a massive 10.5-fold increase in proline content at 3200 Gy, and a hierarchical activation of antioxidant enzymes. SOD activity increased dose-dependently (up to 10-fold), CAT activity was sustainably enhanced, and APX showed a distinct early peak (6-fold increase at 800 Gy). This coordinated response effectively protected membrane integrity against lipid peroxidation up to 1600 Gy, despite substantial H2O2 accumulation. An integrated heatmap visualization summarized this synergistic defense profile. Conclusions The survival of Bracteacoccus sp. under high-dose gamma radiation is underpinned by an integrated, multi-faceted defense strategy. This strategy encompasses growth regulation, photosynthetic apparatus remodeling, orchestrated osmolyte support, and a synergistic antioxidant enzyme cascade. This strain represents a promising eukaryotic model for radiotolerance studies and a potential source of novel radioprotective compounds.