Isolation, identification, and determination of plant growth promoting properties of Azotobacteria isolated from soil samples North-west of Iran under different land-use

Azotobacter is free-living nitrogen-fixing bacteria that it leading to promoting plants growth through various ways. Frequency and distribution of Azotobacter is affected by soil use and its properties. Accordingly, this study aimed to isolate and identify some of plant growth promoting (PGP) Azotobacters. To this end, 50 soil samples were taken randomly from depth 0-25-cm under different land-uses in three provinces viz. Eastern-Azerbaijan, Ardabil and Gilan. Soil paste method was used for isolation of these bacteria and purification was done in LG and NA media. We first isolated 50 bacterial isolates based on the phenotypic and morphological properties. And then we selected nine isolates of them for detailed and deep studies (including 2SP-5, 14SPI, 14SP2-1, 16SP-2, 34SPIII, 35SP, 35SP-2, 43SP-2 and 44SP-2). Results of molecular identification of bacteria (16S rDNA) revealed that among nine isolates, the five isolates (viz. 14SPI, 14SP2-1, 16SP-2, 35SP and 44SP-2) belonged to Azotobacter chroococcum, and isolates 34SPIII and 35SP-2 belonged to Pseudomonas sp. while 2SP-5 and 43SP-2 were identified as Beijerinckia sp. We also found the highest N fixation, and P solubility and auxin production were recorded by A. chroococcum 14SP2-1 and Pseudomonas sp. 34SPIII, respectively. Maximum potassium releasing was observed by A. chroococcum 14SP2-1 and 44SP-2. In this study, all the identified Azotobacteria belonged to A. chroococcum which isolated from the pasture, corn and rice lands of East Azerbaijan and Gilan provinces.