Mycosporine-like Amino Acids Biosynthesis in Asterarcys sp. Driving by Phosphorus Limitation: Evidence from Physiological and Transcriptomic Analyses

Mycosporine-like amino acids (MAAs), a class of secondary metabolites characterized by a cyclohexenone or cyclohexenimine ring structure bound to amino acid residues, are widely distributed in algae. These compounds exhibit strong ultraviolet-absorbing and antioxidant activities, making them attractive candidates for natural sunscreen formulations. However, the low productivity of MAAs in microalgae severely hampers commercial viability. Asterarcys sp., a fast-growing, heat- and light-tolerant microalga, has recently been demonstrated to produce high levels of MAAs under UV irradiation. In this study, phosphorus limitation was found to stimulate rapid MAAs accumulation in Asterarcys sp. SCSIO-46548. After eight days of cultivation, microalgal cells grown in phosphorus-free medium (0 mg L−1) showed a sixfold higher MAAs content (1.08% DW) compared to the group supplied with 5.60 mg L−1 phosphorus (0.18% DW). However, the accumulation of MAAs began to plateau under phosphorus deprivation. Based on integrated homology alignment with cyanobacteria and functional domain validation, a putative biosynthetic pathway for mycosporine-serine in Asterarcys sp. SCSIO-46548 was proposed. Importantly, the gene expression of desmethyl-4-deoxygadusol synthase (DDGS) exhibited a 2.75-fold upregulation under phosphorus limitation. Complementary bioinformatic analyses further characterized the subcellular localization and major physicochemical properties of the candidate enzymes involved. In conclusion, phosphorus limitation is an effective strategy to enhance MAAs production in Asterarcys sp. SCSIO-46548 by upregulating the expression of key biosynthetic genes, such as DDGS. This finding provides an effective solution to the low MAAs productivity in microalgae cultivation.