Isolation and Characterization of Endophytic Exiguobacterium acetylicum from Wild Palm Roots grown in Siwa Oasis and Its Application in Enhancing Wheat Growth Under High Salinity Stress

Soil salinity severely constrains wheat productivity in arid regions. We isolated an endophytic bacterium from wild date palm (Phoenix dactylifera L.) roots collected from the hypersaline Siwa Oasis (Egypt) and was identified by 16S rRNA sequencing as Exiguobacterium acetylicum. The isolate tolerated upto 15% (w/v) NaCl in vitro and expressed multiple plant growth-promoting (PGP) traits, including growth on ACC as the sole N source, phosphate solubilization, indole-3-acetic acid (IAA) production, and ammonification. Nitrogen fixation on JNFb medium was not detected. Colonization of wheat roots and shoots was confirmed by re-isolation and sequencing. In a greenhouse pot experiment in sand culture, plants were grown under four irrigation salinity levels (ECw 0.7, 4, 8, 12 dS m⁻¹) with or without inoculation. Across salinities, inoculation significantly increased biomass and yield components. Under severe salinity (12 dS m⁻¹), inoculated plants showed higher fresh (+42.9%) and dry (+52.1%) biomass, spike weight (+50.7%), and grain weight (+63.5%) relative to non-inoculated controls. Inoculation also maintained higher photosynthetic chlorophyll and carotenoids pigments and lowered proline accumulation (e.g., −33% at 12 dS m⁻¹), indicating mitigation of osmotic/oxidative stress. Grain nutritional quality improved: at 12 dS m⁻¹, grain N, P, and K increased to 2.06%, 0.36%, and 0.58%, respectively, while Na decreased to 0.50% increasing grain protein from 7.94% to 12.88%. Overall, results demonstrate that endophytic E. acetylicum isolated from a saline desert habitat enhanced wheat growth, yield, ionic balance, and grain protein under saline conditions. This isolate represents a promising bioinoculant for biosaline agriculture, warranting multi-site field validation.