Abstract
Haloarchaea are extremophilic microorganisms that in their natural ecosystem encounter several sources of oxidative stress. They have developed different strategies to cope with these harsh environmental conditions, among which bacterioruberin production is a very notable strategy. Bacterioruberin (BR) is a C50 carotenoid synthesized in response to different types of stress. Previous works demonstrated that it shows interesting antioxidant properties with potential applications in biotechnology. In this study, Haloferax mediterranei strain R-4 was exposed to different concentrations of the oxidant compound H2O2 to evaluate the effect on carotenoid production focusing the attention on the synthesis of bacterioruberin. Hfx. mediterranei was able to grow in the presence of H2O2 from 1 mM to 25 mM. Cells produced between 16% and 78% (w/v) more carotenoids under the induced oxidative stress compared to control cultures. HPLC-MS analysis detected BR as the major identified carotenoid and confirmed the gradual increase of BR content as higher concentrations of hydrogen peroxide were added to the medium. These results shed some light on the biological role of bacterioruberin in haloarchaea, provide interesting information about the increase of the cellular pigmentation under oxidative stress conditions and will allow the optimization of the production of this pigment at large scale using these microbes as biofactories.
Highlights
Oxidative stress arises from an imbalance between the production of reactive oxygen (ROS) and nitrogen species (NOS), and the antioxidant mechanisms of the living organism like enzymes or other molecules such as glutathione, vitamins, or pigments [1,2]
At the lowest concentrations (1, 2.5, and 5 mM) growth curves showed the typical behavior expected from standard complex media
This work demonstrates how Hfx. mediterranei cells modulates the synthesis of carotenoids in response to oxidative stress, leading to a gradual increase of the final concentration of bacterioruberin, the most abundant identified carotenoid
Summary
Oxidative stress arises from an imbalance between the production of reactive oxygen (ROS) and nitrogen species (NOS), and the antioxidant mechanisms of the living organism like enzymes (i.e., catalase) or other molecules such as glutathione, vitamins, or pigments [1,2]. Haloarchaea are extremophilic microorganisms that inhabit hypersaline environments since they require mid or high salt concentrations to survive. Their natural ecosystems comprise hypersaline lakes, soils, springs, solar salterns, and rock salt deposits, where the level of salinity is harsh, and other environmental parameters are extreme, such as intense solar radiation and frequent desiccation-hydration cycles [5,6]. Several DNA repair mechanisms [6], synthesis of polymers used as carbon and energy storage (PHA/PHB/PHV) [7,8,9], or hyperpigmentation [6,10,11,12,13,14] can be highlighted
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