Document Type : Original Article

Authors

• Azadeh Haddad Sabzevar ¹
• Mahboobeh Nakhaei Moghaddam ²
• Mohammad Reza Zolfaghari ³

¹ MSc in Microbiology, Department of Biology, Mashhad Branch, Islamic Azad University, Mashhad, Iran

² Assistant professor in Microbiology, Department of Biology, Mashhad Branch, Islamic Azad University, Mashhad, Iran

³ Assistant professor in Microbiology, Department of Microbiology, Qom Branch, Islamic Azad University, Qom, Iran.

Abstract

Rhizobia are well known group of symbiotic bacteria that infect roots of leguminous plants and fix nitrogen. These are facing multiple stresses in the soil that influence growth of bacteria, establishing symbiosis and nitrogen fixation ability. This study aimed to evaluate the tolerance of twenty three isolates of Sinorhizobium meliloti to heavy metals, antibiotics and different concentrations of salinity in Mashhad and Sabzevar. Resistance of isolates to antibiotics was determined by agar diffusion method for penicillin, tetracycline, vancomycin, nalidixic acid. Bacterial resistance to heavy metals, including copper, cadmium, zinc, manganese and various concentrations of sodium chloride, 0.5, 1, 2, 3, and 4% in solid medium was tested. The results showed that 100% of the isolates were resistant to penicillin and susceptible to tetracycline. Inhibitory pattern was different for vancomycin, nalidixic acid, and streptomycin. The isolates were grown at concentrations of 0.5 mmol CuCl₂, 0.65 mmol CdCl₂, 0.125 mmol ZnSO₄ and 1.5 mmol MnSO₄. Results of tolerance to different levels of salinity showed that all isolates had the ability to grow in low concentration of NaCl and only seven isolates had the ability to grow in high concentrations.

Keywords

• Rhizobium
• Symbiosis
• Leguminous
• stress
• Sodium chloride