Genomic and physiological analysis of C₅₀ carotenoid-producing novel Halorubrum ruber sp. nov

A novel haloarchaeal species designated as MBLA0099^T was isolated from seawater near Yeongheung Island. Cells were Gram-negative, non-motile, red-pigmented, and rod-shaped. They grew at 10-45°C, within pH 5.5-9.0, and between 7.5% and 30% NaCl concentrations. Cells were able to grow without Mg²⁺ and were lysed in distilled water. The size of the whole-genome and G + C content of DNA was 3.02 Mb and 68.9 mol%, respectively. Phylogenetic analysis shows that the strain MBLA0099^T belongs to the genus Halorubrum. The average nucleotide and amino acid identity, and in silico DNA-DNA hybridization values were below the species delineation threshold. Pan-genomic analysis revealed that 3.2% of all genes present in strain MBLA0099^T were unique to the strain. The red carotenoid produced by strain MBLA0099^T was subjected to spectrometric and chromatographic analyses and confirmed to be bacterioruberin as C50 carotenoid. Mevalonic acid, terpenoid backbone, and carotenoid biosynthesis pathway were annotated for strain MBLA0099^T. The C50 carotenoid production by strain MBLA0099^T was also enhanced under various stress conditions including relatively netural pH, high oxidative and salinity conditions. Additionally, the strain MBLA0099^T-derived bacterioruberin showed the antioxidant activity with EC₅₀ value of 12.29 µg/ml, based on the evaluation of DPPH free radical scavenging activity. The present study would be the first report on the identification of C₅₀ carotenoid from the strain MBLA0099^T representing a novel species of the genus Halorubrum, for which the name Halorubrum ruber sp. nov. is proposed. The typestrain used was MBLA0099^T (= KCTC 4296^T = JCM 34701^T).