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. 2020 Oct 29;9(11):1060.
doi: 10.3390/antiox9111060.

Carotenoids as a Protection Mechanism against Oxidative Stress in Haloferax mediterranei

Micaela Giani  1 , Rosa María Martínez-Espinosa  1   2
Affiliations

Carotenoids as a Protection Mechanism against Oxidative Stress in Haloferax mediterranei

Micaela Giani et al. Antioxidants (Basel). .

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.

Keywords: H2O2; archaea; bacterioruberin; haloarchaea; hydrogen peroxide; oxidative stress.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
(a) Growth curve of Hfx. Mediterranei cell cultures. Vertical dotted line indicates the time of the H2O2 addition. (b) Specific growth velocity (µ) of Hfx. Mediterranei during exponential phase. From 10 mM to 25 mM, there are two µ values since under these conditions, cells presented a diauxic growth with two exponential phases. Each experimental sample was compared to the control to evaluate statistical significance. *** p < 0.001. **** p < 0.0001.
Figure 2
Figure 2
Growth of preadapted cells vs. growth of non-preadapted cells. Preadapted and non-preadapted Hfx. Mediterranei cell cultures were grown under 5 mM (black) and 15 mM (grey) H2O2 exposure. Vertical dotted line indicates time of the H2O2 addition.
Figure 3
Figure 3
Visual comparison of the acetone extracts obtained from a selection of Hfx. Mediterranei cell cultures exposed to different H2O2 concentrations (0 mM ©), 5 mM, 10 mM, 15 mM, 20 mM, and 25 mM.
Figure 4
Figure 4
BR quantification (µg/mL) from extracts of Hfx. Mediterranei cell cultures exposed to different concentrations of H2O2. Each experimental sample was compared to the control to evaluate statistical significance. *** p < 0.001. **** p < 0.0001.
Figure 5
Figure 5
Relative percentage average of (a) BR and (b) MABR abundance and in Hfx. mediterranei cell cultures exposed to different concentrations of H2O2. Relative percentage was calculated by the sum of each percentage observed in the different peaks per sample in which BR and MABR were detected by its total m/z value: 740.9 and 722, respectively. Each experimental sample was compared to the control to evaluate statistical significance. ** p < 0.005, *** p < 0.001, **** p < 0.0001.
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