Characterization of multicomponent antioxidants from  Haloferax alexandrinus GUSF-1 (KF796625)

The present study was aimed to exploit the haloarchaeon Haloferax alexandrinus GUSF-1 (KF796625) for the presence of biomolecules possessing antioxidant activity. The culture produced a bright orange pigment when grown aerobically in nutrient rich medium with 25% crude solar salt. Biomolecules from cell-free supernatant and from the cells of the culture were individually extracted through the assistance of solvents of different polarities, such as ethanol, methanol and hexane, and monitored for scavenging of stable free radicals. Each of the extracts showed varying capacities to scavenge DPPH^•(20, 31, and 80% DPPH^• RSA; 160.19, 248.29 and 640.76 AAE µg g^-1 of cells) at 1 mg mL^-1. The extracellular ethanolic extract was polysaccharide in nature, equivalent to 47 µg mL^-1 of glucose when assayed with the phenol-sulfuric acid method. The Fourier Transform-Infra Red spectroscopy confirmed the characteristic glycosidic peaks between 2000 and 1000 cm^-1. Similarly, the glycerol diether moiety separated from hydroxylated methanolysates through thin-layer chromatography scavenged free radicals (10.47% DPPH^• RSA; 80.03 AAE µg g^-1 of cells). Further, the hexanolic extract exhibited spectral characteristics of red carotenoids and resolved into distinct compounds when separated by thin-layer chromatography using different developing systems. All separated compounds were positive for the DPPH^• reaction (13-30% DPPH^• RSA; 100-240 AAE µg g^-1). Chemical profiling of the hexanolic extract using the high resolution-liquid chromatography-mass spectroscopy-diode array detector analysis confirmed the presence of different carbon length isoprenoids; C₃₀: tetrahydrosqualene, C₄₀: 3-hydroxyechinenone, astaxanthin, canthaxanthin, lycopene, phytofluene, phytoene and C₅₀: bisanhydrobacterioruberin, monoanhydrobacterioruberin, bacterioruberin and haloxanthin. Thus, we conclude that the synergistic actions of all these components contribute to the antioxidant activity of the culture and that the antioxidant activity of the exopolysaccharide, glycerol dither moiety, tetrahydrosqualene, haloxanthin and 3-hydroxyechinenone is recorded as the first report for Haloferax alexandrinus GUSF-1 (KF796625). Therefore, recommended for use in microbial industrial biotechnology.

The online version contains supplementary material available at 10.1007/s13205-020-02584-9.