Halotolerant plant growth promoting Streptomyces maritimus strain SST3 alleviates salinity stress in Solanum lycopersicum by improving growth, nutritional content and antioxidant enzymes

Soil salinity is one of the most severe environmental stresses that hampers plant growth and crop yield globally. To overcome this, we isolated and characterized the potent halotolerant Streptomyces maritimus strain SST3 from marine sediment. A salt tolerance assay exhibited that strain SST3 could grow in the presence of NaCl up to 1200 mM. This actinobacterial strain showed beneficial plant growth-promoting (PGP) traits at different NaCl concentrations. Strain SST3 produced 5.73 mg mL⁻¹ of exopolysaccharides under 800 mM NaCl stress. The inoculation of strain SST3 under 50–200 mM NaCl stress conditions increased the root length (147–244 %), shoot length (96–226 %), fresh weight (82–303 %), dry weight (43–294 %) and chlorophyll contents (chlorophyll a 40–142 %, chlorophyll b 29–144 % and carotenoids 56–85 %) of Solanum lycopersicum as compared to corresponding uninoculated salt-stressed plants. Strain SST3 maintained a greater K⁺/Na⁺ ratio (0.21–2.14) while decreasing Na⁺ absorption (48–74 %), which mitigated the effects of salt stress on plant growth. The plants inoculated with strain SST3 showed a higher uptake of N (86–167 %), P (74–178 %), Ca (41–85 %), Mg (34–145 %) and Fe (46–125 %) in their leaves than the corresponding uninoculated salt-stressed plants. Furthermore, strain SST3-inoculated plants had reduced malondialdehyde concentrations (41–60 %) and increased catalase (28–147 %), superoxide dismutase (26–134 %) and ascorbate peroxidase (24–97 %) activities under salinity stress. Our findings suggest that utilizing the halotolerant strain SST3 can be an economical and sustainable method of alleviating salinity stress in crop production.