Isolation, Biochemical Characterization and Plant Growth-Promoting Potential of Rhizobacteria from the Soybean Rhizosphere

Abstract

Plant growth-promoting Rhizobacteria (PGPR) are beneficial microorganisms with potential applications in sustainable agriculture. This study aimed to isolate, characterize, and evaluate the plant growth-promoting potential of Rhizobacteria associated with the soybean (Glycine max L.). Rhizosphere soil samples were collected from soybean fields of Dera Ghazi Khan, Punjab, Pakistan, and eight bacterial isolates (SRB-1 to SRB-8) were obtained through culture-based isolation. The isolates were characterized based on morphological and biochemical properties and screened for important PGPR traits, including phosphate solubilization, indole-3-acetic acid (IAA) production, siderophores production, and nitrogen fixation. Considerable diversity was observed among isolates in colony characteristics, Gram reaction, and biochemical profiles. All isolates showed positive catalase activity, nitrate reduction, and carbohydrate utilization. Phosphate solubilization ranged from 11.4 to 23.1 mm, while IAA production varied from 16.9 to 38.5 µg mL⁻¹. SRB-8 exhibited the highest phosphate solubilization index (2.75) and IAA production (38.5 µg mL⁻¹), followed by SRB-4 and SRB-6. Integrated evaluation identified SRB-4, SRB-6, and SRB-8 as superior isolates possessing multiple PGPR traits. These findings highlight the potential of indigenous soybean Rhizobacteria as promising bio fertilizer candidates for enhancing soil fertility and sustainable soybean production.