The endophytic <i>Pseudomonas</i> sp. JBR1 alleviates salt stress through integrated host–microbiome mechanisms

Soil salinity is a major abiotic stress that restricts plant growth and agricultural productivity worldwide. Here, we characterized Pseudomonas sp. JBR1, an endophytic bacterium isolated from the halophyte Carex pumila, and evaluated its capacity to enhance salt tolerance in non-halophytic plants. Inoculation with strain JBR1 markedly improved growth of Arabidopsis (Arabidopsis thaliana) and Brassica rapa under saline conditions by reducing reactive oxygen species accumulation, enhancing antioxidant enzyme activity, improving Na⁺/K⁺ ion homeostasis, and stimulating auxin accumulation in roots. In addition to these direct physiological effects, strain JBR1 markedly altered rhizosphere microbial communities. 16S rRNA amplicon sequencing revealed increased microbial diversity and enrichment of beneficial taxa, particularly Streptomyces and Pseudomonas. Predictive functional profiling indicated upregulation of bacterial motility, chemotaxis, and signal transduction pathways in strain JBR1-treated plants, suggesting enhanced microbial colonization and plant-microbe interactions. These results demonstrate that strain JBR1 confers salt tolerance through a dual mechanism: direct modulation of host physiology and indirect restructuring of the rhizosphere microbiome. The synergistic effects of strain JBR1 highlight its potential as a microbial bioinoculant to improve crop resilience in saline soils and support sustainable agriculture.