Genomic Insights into Bacterioruberin and Halorhodopsin Biosynthetic Genes in 12 Halophilic Archaea Isolated from...

Halophilic archaea are extremophilic microorganisms uniquely adapted to thrive in hypersaline environments such as solar salterns, saline lakes, and brines. Their ability to survive under high-salt conditions is closely associated with the production of unique compounds specifically synthesized by haloarchaea, including bacterioruberin and halorhodopsin. Bacterioruberin is a carotenoid pigment that protects cells from oxidative stress and contributes to osmotic stress resistance. Halorhodopsin is a light-driven Cl^- pump that helps maintain ionic homeostasis. These functional molecules play crucial roles in osmotic stress resistance and energy conversion under extreme conditions. Therefore, understanding their genomic information is essential to uncover the molecular mechanisms underlying their remarkable adaptation and survival in high-salt conditions. In this study, we performed genomic analysis of 12 strains of haloarchaea isolated from Korean solar salterns. Phylogenetic and whole-genome analysis revealed that the isolates are taxonomically distinct from closely related species. The core genes (crtE, crtB, crtI, lyeJ, crtD, and cruF) for bacterioruberin biosynthesis were generally conserved across all analyzed strains, but some strains were found not to possess the crtI gene, and halorhodopsin gene (hop) was identified only in 7 strains. These results show the diversity and conservation of gene distribution related to adaptation to a high-salt environment. As a result, the compensatory role of crtD in the strain lacking the crtI and the lack of the hop in the genus Haloferax were confirmed. These results expand the understanding of the genetic and evolutionary basis associated with adaptation to high-salt environments.