Characterization and Functional Evaluation of Carotenoids From <i>Haloarcula rubripromontorii</i> BS2

Haloarcula rubripromontorii BS2, an extremely halophilic archaeon was obtained from the solar salt pans of Goa, India. It grew luxuriantly on EHM medium with 25% NaCl with a bright orange pigmentation. This study aimed to extract and characterize the carotenoids from Haloarcula rubripromontorii BS2 and evaluate their antioxidant properties, biocompatibility and provide insight into their potential therapeutic applications. Preparative high-performance liquid chromatography (HPLC) was employed to fractionate and separate the haloarchaeal carotenoids. Further detailed characterization using liquid chromatography-mass spectrometry (LC-MS), Raman spectroscopy and nuclear magnetic resonance (NMR) spectroscopy for each fraction confirmed the presence of C50 carotenoids primarily bacterioruberin, monoanhydrobacterioruberin, and their different isomeric forms. Our results indicate that these carotenoids are more stable in oil compared to solvents. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3 ethylbenzothiazoline-6-sulfonic acid (ABTS) assays resulted in an IC₅₀ of 4.31 ± 0.07 µgmL^-1 and 2.04 ± 0.02 µgmL^-1 respectively, indicating their potential as excellent antioxidants. Haloarchaeal carotenoids were found to be biocompatible with human keratinocyte skin cells (HaCaT). C50 carotenoids from Har. rubripromontorii BS2 represent promising, eco-friendly alternatives to synthetic antioxidants for use in high-value cosmetic and dermatological applications.