Abstract

Iron is an essential micronutrient that plays a fundamental role in various physiological and metabolic functions in plants, such as respiration, photosynthesis, enzyme activity, and chlorophyll synthesis. Although iron is naturally present in most soils, it is often found in insoluble forms, particularly in calcareous or alkaline soils, which significantly limits its availability to plants and leads to iron deficiency, negatively affecting crop yield and plant health. This study was conducted to isolate, characterize, and molecularly identify iron-solubilizing bacteria (ISB) from agricultural soils collected in the Erbil Governorate of Iraq. Soil samples were taken from the rhizosphere zones of cultivated plants and inoculated onto King’s B agar medium supplemented with iron oxide (FeO) to detect ISB based on their ability to form clear halos around the colonies, indicating iron solubilization. A total of 114 diverse bacterial isolates were obtained and further characterized using morphological, biochemical, and molecular methods, including 16S rRNA gene sequencing. The isolates were identified as Streptococcus sobrinus (35 strains), Pseudomonas putida (40 strains), and Stenotrophomonas acidaminiphila (39 strains). Among these, two highly efficient isolates, Fe9 and Fe19, demonstrated the highest iron solubilization potential, forming distinct halo zones with solubilization indices (SI) greater than 2.5. Their iron-releasing capacity in liquid culture was also confirmed through precise quantitative analysis using Atomic Absorption Spectroscopy (AAS). The findings suggest that these native, beneficial bacterial strains have strong potential to be developed into environmentally friendly biofertilizers for improving iron availability in soils, thus enhancing plant growth and reducing reliance on synthetic chemical fertilizers in modern sustainable agricultural practices.