Solubilization potential of Bacillus subtilis and Pseudomonas aeruginosa on Phosphorus form in Calcareous Soil

• Neroj Issa Sideq 1, * and Mustafa Ismael Umer2*

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Due to its importance in several physiological and biochemical processes, phosphorus (P) is necessary for all known forms of life. Calcareous soils are one of the major challenges in agriculture due to their high ability to fix phosphorus and make it unavailable to plants. There are rare studies focusing in role of P solubilizing bacteria in calcareous soils in Iraqi Kurdistan Region. This study aims to evaluate the role of Bacillus subtilis and Pseudomonas aeruginosa bacteria as Phosphate solubilizers in calcareous soils amended with organic (sheep manure) and mineral (DAP) fertilizers. The experiment was conducted at the Faculty of Agricultural Engineering Sciences – Duhok University during the period from December 2024 to June 2025, using 22 agricultural pots for wheat cultivation (Jehan classification 99). Two types of soil with different percentages of calcium carbonate (18% and 35%) were used, and bacteria were isolated and diagnosed using PCR techniques,16S rRNA gene sequencing and VITEC 2. Result revealed, 16S rRNA gene sequencing blast revealed strong similarity to Bacillus subtilis (93.65%). The VITIC 2 technique of Pseudomonas aeruginosa gives probability (99%). Total phosphor was recorded significantly (p<0.01) the highest value (1649.112) in the combination Qesrok with DAP. Bcillus subtilis, followed by Qesrok and DAP. Pseudomonas aeruginosa (1456.562). Organic phosphor (OP) was recorded highly significant (p<0.01) the highest value (370.206) in the combination Qesrok and manure. Bacillus subtilis, followed by Korader with DAP (331.913). Available phosphor was recorded significantly (p<0.01) the highest value (68.304) in the combination Qesrok with DAP and Bacillus subtilis, followed by Korader with DAP and Bacillus subtilis (63.013). Bacillus subtilis population was significantly achieved by the combination of Qasrok soil with DAP (13.1710⁶ CFU/g) followed by Pseudomonas aeruginosa (12.4610⁶ CFU /g) in Qasrok soil with DAP.As a conclusion, the substantial synergistic interaction was found with the highly soluble DAP fertilizer and the superior enzymatic activity of Bacillus subtilis.  

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