The genomes of extremophilic microorganisms represent valuable genetic repositories and blueprints for sustainable biotechnological innovations, positioning these organisms as critical drivers of global technological advancement (Antranikian and Streit, 2022). Extreme environments, such as high-altitude saline lakes, are characterized by harsh conditions, including elevated salinity, low temperatures, and limited nutrient availability. These conditions impose intense selective pressures that shape microbial community composition and functionality, consequently fostering significant genetic diversity. Microbial communities inhabiting such extreme ecosystems have evolved specialized physiological and genetic adaptations, rendering them important subjects for microbial taxonomy, ecological studies, and biotechnological exploitation (Triadó-Margarit and Casamayor, 2013). Saline lakes represent globally significant microbial habitats, comprising approximately half of Earth's contemporary lacustrine water bodies (Santini et al., 2022). Therefore, investigating the composition and functional capabilities of microbial communities in hypersaline environments is essential for discovering novel microbial resources with unique metabolic capacities and stress-tolerance mechanisms.

The bacterial genus Gillisia, frequently isolated from extreme environments, exhibits notable halotolerant and psychrophilic properties (Azzaro et al., 2022). Members of this genus play pivotal roles in nutrient-limited ecosystems, particularly through contributions to nitrogen and sulfur biogeochemical cycles (Zhang et al., 2024). Gillisia, classified within the family Flavobacteriaceae, class Flavobacteriia, was initially described by Van Trappen et al. (2004) with the type species Gillisia limnaea. At present, the genus Gillisia comprises eight validly published species names (https://lpsn.dsmz.de/genus/gillisia) (Parte, 2018): Gillisia limnaea (Van Trappen et al., 2004), Gillisia hiemivivida (Bowman and Nichols, 2005), Gillisia illustrilutea (Bowman and Nichols, 2005), Gillisia lutea (Vidal-Verdu et al., 2023), Gillisia marina (Roh et al., 2013), Gillisia mitskevichiae (Nedashkovskaya et al., 2005), Gillisia myxillae (Lee et al., 2006), Gillisia sandarakina (Bowman and Nichols, 2005). Members of the genus Gillisia are characterized as Gram-stain-negative, rod-shaped, strictly aerobic, chemoheterotrophic bacteria displaying moderate halotolerance and psychrophilic growth (Van Trappen et al., 2004). The primary polar lipid in Gillisia species is phosphatidylethanolamine (PE). Dominant cellular fatty acids include iso‐C15:0, iso‐C15:1 G, iso‐C17:0 3-OH and summed feature 3 (C16:1 ω7c/C16:1 ω6c). Gillisia species test positive for catalase activity and negative for oxidase activity, with DNA G + C content ranging between 32.0 and 39.0 mol% (Roh et al., 2013). Despite an increasing number of described Gillisia species, the current understanding of their metabolic capabilities, ecological functions, and adaptive mechanisms-particularly in high-altitude saline lake environments-remains limited and warrants further exploration.

Achikkul Lake, located in the Altun Mountain region of northwest China, is a hypersaline, high-altitude ecosystem that endures extreme environmental conditions, including elevated salinity, low temperatures, and nutrient scarcity. In this study, we describe a novel strain, designated Q332T from the Achikkul Lake. A comprehensive polyphasic approach was employed, including phenotypic, physiological, chemotaxonomic, phylogenetic, and genomic analyses, to determine its taxonomic position and functional traits. Strain Q332T exhibited distinct metabolic capabilities, including nitrate assimilation, carbohydrate metabolism, and stress adaptation mechanisms, which differentiate it from previously described Gillisia species. Whole-genome sequencing and comparative genomic analysis further revealed its potential ecological roles and applications in nitrogen cycling, bioremediation, and adaptation to extreme environments. The study not only enriches our understanding of the genus Gillisia but also highlights the importance of extremophilic bacteria in biogeochemical processes and their potential for biotechnological applications.