Halophilic archaea are a promising natural source of carotenoids. However, little information is available about the biological impacts of these archaeal metabolites. Here, carotenoids of Natrialba sp. M6, which was isolated from Wadi El-Natrun, were produced, purified and identified by Raman spectroscopy, Gc-mass spectrometry, and fourier transform infrared spectroscopy, Lc-mass spectrometry and nuclear magnetic resonance spectroscopy. the c 50 carotenoid bacterioruberin was found to be the predominant compound. Because cancer and viral hepatitis are serious diseases, the anticancer, anti-HcV and anti-HBV potentials of these extracted carotenoids (pigments) were examined for the first time. In vitro results indicated that the caspase-mediated apoptotic anticancer effect of this pigment and its inhibitory efficacy against matrix metalloprotease 9 were significantly higher than those of 5-fluorouracil. Furthermore, the extracted pigment exhibited significantly stronger activity for eliminating HcV and HBV in infected human blood mononuclear cells than currently used drugs. this antiviral activity may be attributed to its inhibitory potential against HcV RnA and HBV DnA polymerases, which thereby suppresses HcV and HBV replication, as indicated by a high viral clearance % in the treated cells. These novel findings suggest that the C 50 carotenoid of Natrialba sp. M6 can be used as an alternative source of natural metabolites that confer potent anticancer and antiviral activities. Halophilic archaea (haloarchaea) belong to the family Halobacteriaceae. This family includes a group of microorganisms that are able to live in hypersaline environments with high salt concentrations (up to 4 M), such as solar salterns, salt lakes and salt deposits 1. Interestingly, these organisms have received increasing attention due to their ability to produce a plethora of compounds with potential applications in many fields of biotechnology, including salt-tolerant enzymes, biodegradable polyesters, exopolysaccharides, antimicrobial halocins, biosurfactants, and photon-driven retinal protein 2. Most haloarchaeal species (e.g., Natrialba) can produce pigments, including carotenoids. Natrialba is an organism in our research that belongs to the Halobacteriaceae family. However, the genus has recently been reassigned to the novel family Natrialbaceae 3. Natrialba sp. M6 is an extreme haloalkaliphile that grows at pH 10.0 and 20-25% w/v NaCl and utilizes a wide range of carbohydrate and noncarbohydrate substrates. Carotenoids are lipid-soluble pigments that vary in colour between yellow, orange, and red. Carotenoids are classified based on the number of carbons in their backbones into the categories C 30 , C 40 and C 50. Most carotenoids exist as a C 40 structure in different living organisms, including bacteria, archaea, fungi, algae, and plants 4. Meanwhile, haloarchaea can produce C 50 bacterioruberin (BR), a rare carotenoid form that contains four hydroxyl groups 5. These pigments are divided into two major groups: xanthophylls (molecu...
