Potential of Locally-Isolated Acinetobacter baumannii Strains as Phosphate Solubilizer from Three Major Onion-Producing Provinces in the Philippines

The fixed insoluble Phosphorus in the soil limits its utilization by crops and thus, the role of phosphate solubilizing bacteria (PSB) is beneficial to increase the P availability in the soil for crops. In order to obtain native isolates that may be used for onion production, three (3) major onion-producing provinces in the Philippines were selected to collect soil samples. A laboratory experiment was carried out to isolate probable PSB employing Pikovskaya (PK) medium with tricalcium phosphate. From a total of 157 isolates that showed a halo zone on PK plates, three (3) representative isolates (one from each location) were selected based on their population dominance and halo zone size for genetic identification using 16S rRNA sequencing. The isolated PSB strains from the three sites showed highly similar nucleotide sequences with Acinetobacter baumannii. In terms of ability to solubilize Phosphorus, the Mindoro Occidental isolate (MOc PSB-RGL-2023) showed the highest solubilizing index of 3.42 mm, followed by Ilocos Sur (IS PSB-RGL-2023) with 3.2 mm, and Nueva Ecija (NE PSB-RGL-2023) with 2.7 mm. These findings suggest the potential of Acinetobacter baumanii as bioinoculant for improving P availability. This study provides a valuable insight as the pioneer report that isolated and characterized possible A. baumannii strains from the three provinces in the Philippines as a prospective PSB bioinoculant.