Isolation and Identification of 10 Strains of Potassium, Phosphorus and Iron Solubilizing Bacteria from the Soil around the Potato Roots in Hamedan Province

About 98 % of the soil's potassium is in the form of minerals that are not available to plants. On the other hand, the continues use of fertilizers has unintended consequences for different habitats. Acid producing microorganisms can transform silicate minerals that contain potassium and release available potassium for plants. The aim of this study was to isolate and identify potassium, phosphorus and iron solubilizing bacteria from the minerals of these elements (potassium silicate, tricalcium phosphate, and hematite) from the soil around potato roots in order to make biofertilizers from plant growth-promoting bacteria.

Potassium solubilizing bacteria were isolated from the soil around potato roots. The isolates were tested and selected in terms of their ability to release potassium from three minerals (biotite, muscovite, and feldspar potassium) qualitatively by spot cultivation based on the emergence of the halo (Halo method) or changing the color of Aleksandrov medium. Then, to estimate the ability of the isolates for releasing potassium, they were cultured in Aleksandrov liquid medium. To investigate the ability for solubilizing t minerals,ricalcium phosphate the isolates were cultured in the same way as described above, but in the Pikovskaya medium. To investigate the ability for solubilizing iron, the modified Pikovskaya medium with hematite mineral was used. This study was performed by a completely randomized factorial design, in which, the minerals used in three levels (muscovite, biotite and feldspar potassium) were the first factor and 30 bacterial isolates were the second factor to release potassium. To analyze the release of phosphorus and iron, a completely randomized design was used and only the ability of 30 isolates for solubilizing of one mineral (tricalcium phosphate or hematite) was tested separately. Statistical analysis was performed with SAS software. Isolates were examined and identified using morphological, biochemical and molecular tests. Then, 10 superior isolates were identified and the plant growth promoting ability tests were performed on them.

Among 30 isolates, 10 top isolates were separated and identified for potassium, phosphorus and iron releasing ability. Flame photometric studies showed that the amount of potassium released by the isolates in the medium containing biotite was 647.18 mg/kg from control to 5416.16 mg/kg from number 10, in the medium containing muscovite was 148.68mg/kg from number21 to 2026.36 mg/kg from number 10, and in the medium containing potassium feldspar was 132.76 from number 7 to 534.88 mg/kg from number 19. The amount of phosphorus released by the isolates was 3582.85 mg/kg from control to 37011.42 mg/kg from number 25 and the amount of iron was 830.00 mg/kg from number 33 to 2661.66 mg/kg from number 4. In this study the released potassium from biotite and feldspar minerals by bacterial isolates was the highest and the lowest one, respectively. There was a high correlation between bacterial acid production and solubilizing minerals ability.

10 top isolates were separated and identified from the soil around potato roots based on evaluating potassium, phosphorus and iron releasing ability. In addition to being potent for releasing potassium, these isolates were also capable of producing auxin and siderophores, and also inhibiting pathogenic fungi (which are characteristics of PGPR bacteria). It is suggested to utilize these isolated bacteria in the production of biofertilizers to increase the bioavailability of potassium, phosphorus and iron for plants and to improve the growth and productivity of crops, especially potatoes.