Salt-tolerant endophytic bacteria from Suaeda aralocaspica enhance tomato growth under salinity stress

Suaeda aralocaspica is an annual halophyte that uniquely thrives in a saline niche with high salt concentrations. However, the role and mechanisms of endophytes in S. aralocaspica remain poorly understood. This study was aimed to explore the growth promoting potential of salt tolerant endophytic bacteria isolated from S. aralocaspica and to clarify their role in enhancing tomato tolerance to salinity. To understand this mechanism, we carried out transcriptomic and metabolomic analyses on leaf tissues of Solanum lycopersicum exposed to salinity stress following bacterial inoculation. Our results showed that 77 out of 96 isolates (80.21 %) of endophytic bacteria exhibited at least one plant growth-promoting trait, including nitrogen fixation, phosphate solubilization, and proteases production. Two representative strains, Streptomyces olivaceus EGI P1B035 and Priestia filamentosa EGI P1B048, were selected for further evaluation. Inoculation with these strains significantly improved tomato seed germination potential and seedling growth under 0–100 mmol/L NaCl. Further these strains markedly increased stem and root length, as well as the fresh and dry weight under salt stress. Furthermore, the bacterial inoculation of these strains significantly enhanced the activity of superoxide dismutase (SOD) and catalase (CAT), increased proline (Pro) and glutathione (GSH) accumulation, and reduced the activity of peroxidase (POD), and malondialdehyde (MDA) contents in S. lycopersicum, indicating improved antioxidant capacity and membrane stability. Integrated transcriptomic and metabolomic analyses indicated that flavonoid biosynthesis and plant hormone signal transduction pathways were predominantly regulated, suggesting their key roles in endophyte-mediated salt tolerance. Finally, our findings demonstrate that S. aralocaspica endophytic bacteria enhance tomato tolerance to salinity through coordinated physiological, transcriptional, and metabolic regulation, providing valuable microbial resources and a solid theoretical basis for developing salt-tolerant microbial agents for agricultural applications.