Isolation, screening and identification of growth-promoting rhizobacteria resistant to abiotic stresses from the microbiome of Alfalfa (Medicago sativa) in saline and arid soils in Kerman province

The purpose of this study is to investigate the characteristics of plant growth promoting rhizobacteria that stimulate plant growth, such as biological nitrogen fixation, phosphate solubilization, and produce hydrogen cyanide and exopolysaccharides, to prepare suitable and efficient biofertilizers. In this research, 135 Rhizobacteria strains were isolated, screened and identified from saline and arid soils in Kerman Province, and some of their growth-promoting characteristics were studied. The Rhizobacteria strains were studied with respect to their ability to fix nitrogen, solubilize insoluble organic and inorganic phosphates in solid and liquid culture media, and produce hydrogen cyanide and exopolysaccharides. Their growth at various sodium chloride concentrations (0, 1, 3, and 5%) and at different polyethylene glycol 6000 concentrations (water potential 0, -1, -2, and -3.5 MPa) was also investigated. According to the results, 72% and 76% of the Rhizobacteria strains exhibited almost no growth at 5% sodium chloride concentration and at water potential -3.5 MPa, respectively. In addition, 50% of them were able to produce hydrogen cyanide under saline conditions. Three of the strains (SM16, SM65, and SM89) were the most efficient producers of exopolysaccharides and had high phosphate solubilization ability (102, 98.5 and 121.7 mL/L, respectively) and were also among Rhizobacteria strains resistant to abiotic stresses. Three strain safe and efficient strains can have great potential to be used as a high quality biofertilizer for improving growth of crop plants in the region.