Physiological Responses of Tomato (Solanum lycopersicum L.) to Salt Stress Mediated by Native Halotolerant Bacillus spp. Strains using LC-MS/MS

Background and aims Climate change is increasing global land salinity, causing plant deterioration, stunted growth, nutrient imbalances, ion toxicity, and physiological disruption. This study explores the potential of halotolerant PGPB (Plant Growth-Promoting Bacteria) particularly Bacillus species, to alleviate salinity stress in tomato plant physiology. Material and methods Two halotolerant strains, Bacillus albus strain FA26 and Bacillus anthracis LOS6, were isolated from dominant plant species in saline regions. Greenhouse experiments were conducted on tomato plants exposed to 200 mM NaCl with and without bacterial inoculation. The key physiological parameters assessed included K ⁺ , Na ⁺ , and Ca ²⁺ concentrations (determined by flame photometry and atomic absorption spectroscopy), chlorophyll content (measured by spectrophotometry), and proline levels (determined by a ninhydrin colorimetric assay). Metabolic profiling of phenolic compounds was performed using Fourier-Transform Infrared spectroscopy (FT-IR) and Liquid Chromatography–Mass Spectrometry (LC-MS/MS). Key results Inoculated plants, improved K ⁺ /Na ⁺ homeostasis under saline conditions, and reduced Na ⁺ accumulation (approximately 66.70% with Bacillus anthracis LOS6). Treatment with Bacillus spp. improved chlorophyll content, while Bacillus albus strain FA26 showed the highest total chlorophyll (42.12 mg L⁻¹), chlorophyll A (23.21 mg L⁻¹), and chlorophyll B (16.34 mg L⁻¹) contents, indicating improved photosynthetic efficiency, also supported proline osmotic adjustment under salt-stressed conditions. proline accumulation increased, with the Bacillus anthracis LOS6 strain showing the highest concentration (5052 µg g⁻¹), representing an increase of approximately 10,43% compared to non-stress conditions, reflecting its strong role in osmotic adjustment and stress tolerance. Secondary metabolites facilitate defense gene activation through salicylic acid biosynthesis. Conclusion These findings highlight the importance of using halotolerant PGPB as a strategy to address salt stress challenges in agriculture, demonstrating their potential to alleviate the adverse effects of salinity stress on tomato plant physiology.