Evaluation of the Ability of Rhizobacterial Isolates to Solubilize Sparingly Soluble Iron Under In-vitro Conditions

Abstract

One of the problems of calcareous soils is the lack of absorbable iron for plants grown in these areas. Research by various researchers has shown that some rhizosphere-dwelling microorganisms have the ability to solubilize resources containing low-soluble iron and conversion it to soluble and absorbable for the plants. Different mechanisms such as proton secretion, production of organic acids, and production of siderophore can be effective in solubilizing low-soluble iron. Accordingly, in this study, the potential of twenty rhizobacteria for solubilizing low-soluble iron sources (eg, iron phosphate, hematite, and goethite) has been evaluated. The experiment was performed under in-vitro condition in a completely randomized design with three replications. According to the results, three isolates, namely, ZP15, ZC10, and ZP13 were characterized as promising isolates. In the presence of iron phosphate, the concentration of solubilized iron by isolates ZP15, ZP13, and ZC10 was 5.19, 4.35, and 4.27 mg/l, respectively. These values for the isolates ZC10 and ZP13 in the presence of hematite was recorded 6.49 and 5.35 mg/l, respectively, and in the presence of goethite was 7.02 and 6.70 mg/l, respectively. The amount of siderophore production for the three isolates ZP15, ZC10, and ZP13 was 16.47, 17.1, and 31.55 µM, respectively. The high-performance liquid chromatography analysis revealed that the most important acids produced by these isolates were 2-ketogluconic acid (303.8 µg/ml) for ZP15, oxalic acid (246.9 µg/ml) for ZC10, and gluconic acid (100.2 µg/ml) for ZP13, respectively. The molecular and biochemical identification of these three isolates ZP15, ZC10, and ZP13 showed that they belong to the genera Stenotrophomonas, Pantoea, and Agromyces, respectively.