Gracilimonas qinghaiensis sp. nov., a halophilic bacterium from a high-altitude saline lake exhibiting diverse metabolic potential and ecological adaptation.

Saline lakes are extreme habitats that host unique microbial communities with high biotechnological potential. In this study, a novel strain, designated Q87(T), was isolated from Gaxiukule Lake, a high-altitude magnesium sulfate-type saline lake in the Qaidam Basin, China. A polyphasic taxonomic approach, including morphological, physiological, chemotaxonomic, phylogenetic, and genomic analyses, was applied to characterize the isolate. Strain Q87(T) is a Gram-stain-negative, non-motile, rod-shaped bacterium showing high tolerance to salinity (0-15.0 %, w/v; optimum 5.0 %) and alkalinity (pH 6.0-10.5; optimum pH 7.0), with a temperature range for growth of 10-40 °C (optimum 32 °C). Phylogenetic and genomic analyses confirmed its affiliation with the genus Gracilimonas and revealed it as a distinct species. The genome of strain Q87(T) (3.3 Mb, G + C 41.5 %) encodes diverse functional genes associated with nitrogen and sulfur metabolism, stress adaptation, and biosynthesis of secondary metabolites, including terpenoids and polyketides. Comparative analyses with reference Gracilimonas strains demonstrated its unique genomic features and ecological adaptability. Structural modeling confirmed functional conservation of key enzymes involved in nitrogen detoxification and sulfide oxidation. Pangenome analysis highlighted the genetic diversity and open nature of the species of the genus Gracilimonas. Biogeographic assessments suggest a wide distribution of the genus in saline environments, especially in sediments. This study expands our understanding of the genus Gracilimonas taxonomy, physiology, and ecological potential, and underscores the importance of extremophilic bacteria as promising resources for environmental and industrial biotechnology.