New Strains of Serratia sp. from the Rhizosphere of Atriplex prostrata Demonstrate Plant Growth-Promoting Properties and Salt Tolerance

In a changing climate, sustainable agriculture urgently requires environmentally friendly solutions. Increasing soil salinity severely limits crop productivity, as excess salts induce osmotic and ion-specific toxicity in plants. A promising strategy for mitigating these effects and enhancing plant salt tolerance involves the use of biofertilizers based on plant growth-promoting (PGP) rhizobacteria. In this study, novel salt-tolerant PGP strains were isolated and characterized from the rhizosphere of the halophyte Atriplex prostrata grown in soils with varying salinity levels. Twelve isolates were screened for key PGP traits, including indole-3-acetic acid (IAA) production, phosphate solubilization, siderophore synthesis, and NaCl tolerance. Two strains, AP9 and AP12, demonstrated the most comprehensive PGP potential. Based on 16S rRNA gene sequencing, they were identified as members of the genus Serratia. In an experiment under salt stress (75, 150, and 225 mM NaCl), inoculation of wheat (Triticum aestivum L.) seeds with these strains significantly improved germination rates and stimulated root and shoot development. The treated plants also exhibited reduced levels of key oxidative stress markers—malondialdehyde (MDA) and proline. Thus, the Serratia sp. AP9 and AP12 strains exhibit pronounced PGP activity and efficacy in enhancing the salt tolerance of wheat. These results indicate that these isolates are promising candidates for the development of novel biofertilizers for sustainable agriculture on saline soils.