Potential of Serratia sp. KF23 in stimulating soybean growth and alleviating the effects of salinity stress in a three-year pot experiment

Abstract Soil salinity may constitute a serious limitation to soybean ( Glycine max L. Merr.) production. In the present study, a halotolerant bacterial strain KF23 was isolated and characterized, and its ability to support soybean growth under salinity stress conditions was evaluated. KF23 exhibited moderate salt tolerance (6% NaCl) and tolerated a wide range of pH (6–10) and temperature (6–42 °C). Subsequently, 16 S rRNA analysis showed that strain KF23 belongs to the genus Serratia and is closely related to Serratia plymuthica . Serratia sp. KF23 produced indole-3-acetic acid, siderophores and NH 3 , exhibited nitrogen fixation and ZnSO 4 solubilization, as well as proteolytic and β-1,3-glucanase activity. KF23 formed biofilm and exopolysaccharides at 0–6% NaCl. In a three-year pot experiment, soybean plants were grown under 0, 150, and 300 mM NaCl with or without KF23 inoculation. KF23 inoculation improved soybean growth at 150 and 300 mM NaCl, increasing root length (+ 32–39.6%), shoot fresh weight (+ 9.8–45.1%), shoot dry weight (+ 19.1–23.3%), and fresh pod weight (+ 23.3–36.9%) relative to the control. Chlorophyll a and b content was higher in inoculated plants, whereas the levels of malondialdehyde, hydrogen peroxide, and proline were lower, indicating a reduction of osmotic and oxidative stress. Catalase activity increased significantly (+ 157.6% at 0 mM and + 20% at 150 mM NaCl). In the soil, a higher total nitrogen concentration was recorded at 300 mM NaCl (+ 11.4%), and dehydrogenase activity remained stable. KF23 also increased protein content and digestibility of soybean above-ground biomass under salinity conditions. The results indicate that Serratia sp. KF23 is a promising plant growth-promoting bacterium improving plant performance and soil quality under salt stress conditions.