Streptomyces longbaonensis sp. nov., a novel actinomycete from an alpine meadow that enhances plant salt tolerance via antioxidative and osmotic regulation

• A novel actinomycete strain, Streptomyces longbaomeadowicum sp. nov. (strain Qhu-M48) from alpine meadow soil on the Qinghai–Tibet Plateau was characterized by polyphasic taxonomy and genome-based metrics. • Genome analysis revealed 31 biosynthetic gene clusters and multiple genes associated with plant growth promotion and stress adaptation. • Inoculation with Qhu-M48 significantly enhanced growth and salt tolerance in oat and sainfoin seedlings. • Qhu-M48 modulates antioxidant enzyme activity and osmolyte accumulation, mitigating oxidative damage in sainfoin seedlings under salt stress. Soil salinization poses a significant threat to plant growth and agricultural yield. Harnessing the potential of plant growth-promoting rhizobacteria (PGPR) emerges as a promising strategy to bolster plant development and enhance tolerance to salt stress. In the present investigation, a novel actinomycete strain Qhu-M48, derived from alpine meadow soil on the Qinghai–Tibet Plateau, was subjected to comprehensive taxonomic characterization. Phylogenetic analysis based on the 16S rRNA gene revealed that strain Qhu-M48 shared the highest sequence similarity (99.63%) with Streptomyces exfoliatus NRRL B-2924 T . However, genome-based taxonomic indices, including dDDH (37.80%) and ANI (88.88%), clearly delineate Qhu-M48 as representing a novel species within the genus Streptomyces . Accordingly, the name Streptomyces longbaomeadowicum sp. nov. is proposed for this novel taxon. Whole-genome analysis uncovered 31 BGCs producing secondary metabolites, along with an extensive repertoire of genes linked to plant growth-promoting traits. Functional evaluation demonstrated that Qhu-M48 significantly promoted the growth of oat and sainfoin seedlings under salt conditions, as evidenced by improved biomass, shoot and root length, relative water content, and photosynthetic efficiency. Biochemical assays indicated that Qhu-M48 enhanced salt tolerance in sainfoin by elevating the activities of antioxidant enzymes, promoting the accumulation of osmoprotectants, and alleviating oxidative stress, as evidenced by reduced levels of peroxides. Collectively, this study describes the comprehensive characterization of a novel actinomycete species endowed with robust plant growth-promoting and salt stress-mitigating properties, offering a promising microbial resource for the development of salt-tolerant bioinoculants. The novel Streptomyces sp. Qhu-M48 promotes growth and enhances salt stress tolerance in oat and sainfoin by boosting biomass, photosynthetic efficiency, and antioxidant defenses, highlighting its potential as a bioinoculant for improving crop resilience under saline conditions.