Photoprotective Responses of Nostoc sphaeroides to UV-B Radiation: Role of Mycosporine-like Amino Acids

Ultraviolet-B (UV-B) radiation (280–315 nm), a component of solar radiation, can negatively affect aquatic microorganisms, including cyanobacteria. To counteract UV-induced damage, cyanobacteria produce mycosporine-like amino acids (MAAs), which function as natural sunscreens and hold potential for use in cosmetics and biomedical products. This study explores the physiological and biochemical responses of the freshwater cyanobacterium Nostoc sphaeroides to low-intensity UV-B exposure. Results showed a decline in photosynthetic activity, indicating stress. However, a significant increase in MAA production was observed, suggesting a protective adaptation. Using high-performance liquid chromatography (HPLC) and mass spectrometry, shinorine was identified as the primary MAA synthesized in response to UV-B. Its accumulation indicates a key role in shielding the organism from UV-B-induced damage. These findings highlight N. sphaeroides as a promising natural source of shinorine, with potential applications in the development of eco-friendly UV-protective agents. Moreover, the study contributes to a better understanding of how cyanobacteria adapt to environmental stress and reinforces the biotechnological relevance of MAAs.