Isolation and identification of potassium-solubilizing bacteria from the rhizosphere of different plants of the Neishabur region and determine their potential for increasing corn growth and development

Potassium, such as nitrogen and phosphorus, is a macronutrient that plays an important role in plant growth. Large amounts of potassium in the soils comes from the silicate minerals such as phyllosilicate minerals. Potassium in the structure of silicate minerals is not available for plants. Inoculation of potassium solubilizing bacteria as biofertilizers is one of the most important biological approaches to provide potassium for plants. The study aimed to isolate, select, and identify the most efficient potassium solubilizing bacteria and their effect on the availability of potassium in a soil amended with biotite.

In the present study, 15 isolates of bacteria from rhizosphere of five different plants (wheat, tomato, alfalfa, corn and basil) were isolated and purified. The determination of potassium solubility of isolates was performed in two separate parts. In the first part, the solubility of potassium by bacterial isolates in liquid Alexandrove culture medium was performed in a completely randomized design with the factorial arrangement in three replications. Experimental factors included 15 bacterial isolates and 3 incubation times (7, 14 and 21 days). The second part of the study was conducted in a completely randomized design to evaluate the effect of selective isolates of potassium-solubilizing bacteria on the growth of single cross cultivar 640 maize in a soil with sandy loam texture class. Experimental treatments included positive control (potassium sulfate fertilizer (SK)), negative control (soil without fertilizer (S)), 2500 mg/kg biotite (SM1), 5000 mg/kg biotite (SM2), B5 isolate + SM1 (SM1B5), B11 isolate + SM1 (SM1B11), B13 isolate + SM1 (SM1B13), B5 isolate + SM2 (SM2B5), B11 isolate + SM2 (SM2B11), and B13 isolate + SM2 (SM2B13). Data analysis was performed using JMP 8 software and the comparison of means was performed using the Tukey test at a probability level of 5% and graphs were drawn with Excel software.

The results of the first part showed that the highest potassium content (16.4 mg / l) and the lowest pH (3.04) belonged to B11 isolates after 21 days of incubation. The results of the second part showed that The highest potassium concentration of shoot (2.81%) and root (0.956%) was observed in potassium sulfate fertilizer treatment (SK) and SM2B11 treatments, respectively. Plant height, green index, and dry weight were higher in the bacterial treatments compare to the negative control. Based on this, the B11 isolate was selected as the superior isolate. Finally, the superior isolate was identified using 16SrRNA gene sequencing and 99.37% was similar to Paenibacillus stellifer.

This study showed that potassium solubilizing bacteria can release potassium from the mineral biotite in both laboratory and greenhouse. In both experiments, B11 (Paenibacillus stellifer) isolate had the greatest effect on the release of mineral potassium from the mineral biotite. Therefore, its use as a biofertilizer is recommended.