Concomitant production of exopolysaccharides and carotenoids by the UVC-resistant bacterium Kocuria rosea CV6

The current work investigates the potential of exopolysaccharides (EPSs) and carotenoids produced from radioresistant bacteria as radioprotective agents. Twenty strains, isolated from gamma-irradiated roots of Cistanche violacea from Chott El-Djerid (Tunisia), were screened for EPSs and carotenoids production. The most EPS and carotenoids-producing bacterium was selected. The assessment of the impact of UVC-radiation dose effects on the synthesis of EPSs and carotenoids was investigated by response surface methodology (RSM). Both EPS and Carotenoids, from the strain CV6, were characterized by UV–Vis and Fourier transform infrared. The radioprotective potential of EPS and carotenoids on the survival of K. rosea CV6 following UVC dose was evaluated using the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide assay. Finally, in silico analyses of CV6’s genome were assessed to identify the mechanisms involved in UVC protection. It was demonstrated that UVC irradiation of Kocuria rosea CV6 generated high amounts of EPSs and a carotenoid-producing strain. The assessment of the impact of radiation dose effects on the synthesis of EPSs and carotenoids by RSM shows that strain CV6 exhibited particular resistance to UVC radiation. The characterization of EPSs revealed the presence of six particular functional groups using Fourier transform infrared spectra. Pigments produced by CV6 were classified as carotenoids based on their spectroscopic characteristics. Also, the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide survival assay demonstrated a positive correlation between the concentrations of EPSs and carotenoids and viability of the UV-sensitive strain, Escherichia coli DH5α, following exposure to UVC radiation. In addition, the whole-genome analysis of the CV6 strain identified seven biosynthetic gene clusters encoding secondary metabolites, including those involved in the synthesis of EPSs and carotenoids. The present investigation demonstrated that EPSs and carotenoids, extracted from K. rosea CV6, are promising bioactive components that could be used in the protection against UVC radiation.