Steppe-Derived Glyphosate-Tolerant Pseudomonas sp. ADL-13 and Paenibacillus sp. ZHS-9 Strains with Plant Growth-Promoting Traits and Broad Abiotic Stress Tolerance

The integration of plant growth-promoting bacteria (PGPB) into sustainable agricultural practices represents a promising strategy for improving crop productivity and stress resilience. We characterized two newly isolated steppe-derived, glyphosate-tolerant bacteria, Pseudomonas sp. ADL-13 and Paenibacillus sp. ZHS-9, evaluating their in vitro glyphosate tolerance, PGP potential, and eco-physiological resilience. Pseudomonas sp. ADL-13 exhibited in vitro glyphosate tolerance, displaying significant growth stimulation at glyphosate concentrations of 1.0–2.0 g/L. Paenibacillus sp. ZHS-9 tolerated glyphosate in vitro up to 0.5 g/L without significant growth inhibition while maintaining measurable growth at 1.0 and 2.0 g/L. In wheat seedlings bioassays, cell-free culture filtrates promoted seedling growth, while inoculation with living cultures significantly enhanced biomass accumulation, seedling growth, and vigor. Plant growth-promoting (PGP) traits included P and K solubilization, and siderophore and ammonia production across strains; additionally, putative nitrogen-fixing potential, and IAA-like indolic compounds were detected in ZHS-9. Furthermore, both isolates demonstrated broad tolerance to saline, osmotic and oxidative stresses, pH and temperature fluctuations. Compatibility assays revealed antagonistic activity of ADL-13 toward ZHS-9, emphasizing the importance of evaluating strain interactions. Collectively, these findings indicate that ADL-13 and ZHS-9 are potential PGPB candidates for further evaluation in agricultural applications.