A set of 110 extremely halophilic archaeal strains were isolated from seven distinct saline habitats located in different regions of Algeria. The physicochemical characterization of the samples showed that these habitats were thalassohaline. The carotenoid production from isolated strains varied from 0.1 to 3.68 µg/ml. Based on their physiological characteristics and pigment production, 43 strains were selected and identified by means of phenotypic tests and 16S ribosomal RNA gene sequencing. Phylogenetic analysis indicated that the isolates corresponded to the class Halobacteria and were closely related to genera Halorubrum, Haloarcula, Haloferax, Natrinema, Halogeometricum, Haloterrigena, and Halopiger. Carotenoids of the highest producer, strain Halorubrum sp. BS2 were identified using high‐performance liquid chromatography–diode array detector and liquid chromatography–mass spectrometry. Bacterioruberin and bisanhydrobacterioruberin were the predominant carotenoids. The scavenging activity of these carotenoids reached 99% at a concentration of 18 μg/ml, which was much higher than that of ascorbic acid used as a reference compound. These carotenoids also exhibited significant antibacterial activities against four human‐pathogenic strains and four fish‐pathogenic strains. Variations in salinity, agitation rate, temperature, and light intensity were found to influence growth and carotenoid production of Halorubrum sp. BS2. Our results suggest that halophilic archaea represent a potential source for carotenoids, which are characterized by high antioxidant and antibacterial activities.

Halophilic archaea represent a promising natural source of carotenoids. However, little information is available about these archaeal metabolites and their biological effects. In the present work, carotenoids of strains Haloferax sp. ME16, Halogeometricum sp. ME3 and Haloarcula sp. BT9, isolated from Algerian salt lakes, were produced, extracted and identified by high-performance liquid chromatography-diode array detector and liquid chromatography-mass spectrometry. Analytical results revealed a variation in the composition depending on the strain with a predominance of bacterioruberin. The evaluation of antioxidant capacity using ABTS [(2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)] and DPPH (2,2-diphenyl-1-picrylhydrazyl) assays showed that these extracts have a strong antioxidant potential, in particular those of Haloferax sp. ME16 which displayed antioxidant power significantly higher than that of ascorbic acid used as standard. Antibacterial activity of carotenoid extracts against four human-pathogenic strains and four fish-pathogenic strains was evaluated by agar disk diffusion method. The results showed a good antibacterial activity. These findings suggest that the C 50 carotenoids from the studied strains offer promising prospects for biotechnological applications.