Exopolysaccharides as novel cryoprotectants released by Antarctic Chlamydomonas sp. ASYA25.

Long-term preservation of microalgae cultures is of great importance for the sustainable production of valuable metabolites. Cryopreservation techniques primarily ensure this continuity, and the effectiveness and toxicity level of cryoprotectant agents used in these techniques play a crucial role in determining the viability of cultures. However, the toxic effects of commonly used chemical agents such as DMSO, MeOH, and glycerol make it necessary to search for environmentally friendly and biocompatible alternatives. In this context, the potential of exopolysaccharides (EPS) derived from psychrotolerant Chlamydomonas sp. ASYA25, as a natural cryoprotectant, was evaluated for the first time in this study. EPS production was optimized using a Plackett-Burman design, and structural characterization was performed using FTIR, UV-Vis, TGA, ICP-MS, HPLC, and NMR. The obtained EPSs were tested in cryopreservation experiments on five different strains of Antarctic microalgae. In a study of 5 % and 10 % EPS with 5 % DMSO, MeOH, and glycerol, the best growth recovery was with 5 % EPS in C. vulgaris ASYA27. Cellular viability was assessed via specific growth rates and Trypan blue staining; EPSs showed low toxicity and preserved cell membrane integrity. The results reveal that microalgae-based EPSs are a promising alternative for conserving extremophilic species and developing sustainable cryoprotectant processes.