Bacterioruberin: Biosynthesis, Antioxidant Activity, and Therapeutic Applications in Cancer and Immune Pathologies.

Halophilic archaea, also termed haloarchaea, are a group of moderate and extreme halophilic microorganisms that constitute the major microbial populations in hypersaline environments. In these ecosystems, mainly aquatic, haloarchaea are constantly exposed to ionic and oxidative stress due to saturated salt concentrations and high incidences of UV radiation (mainly in summer). To survive under these harsh conditions, haloarchaea have developed molecular adaptations including hyperpigmentation. Regarding pigmentation, haloarchaeal species mainly synthesise the rare C50 carotenoid called bacterioruberin (BR) and its derivatives, monoanhydrobacterioruberin and bisanhydrobacterioruberin. Due to their colours and extraordinary antioxidant properties, BR and its derivatives have been the aim of research in several research groups all over the world during the last decade. This review aims to summarise the most relevant characteristics of BR and its derivatives as well as describe their reported antitumoral, immunomodulatory, and antioxidant biological activities. Based on their biological activities, these carotenoids can be considered promising natural biomolecules that could be used as tools to design new strategies and/or pharmaceutical formulas to fight against cancer, promote immunomodulation, or preserve skin health, among other potential uses.