Isolation and Characterization of Acinetobacter baumannii from Soils of Three Major Onion-Producing Provinces in the Philippines

One of the key strategies for sustainable agriculture is the utilization of indigenous soil microorganisms as inoculant. In this report, three major onion-growing provinces in the Philippines were identified and soils were collected for the isolation of beneficial microorganisms which were characterized for potential to be used as inoculant, particularly as phosphate solubilizer. A laboratory experiment was carried out to isolate potential phosphate solubilizing bacteria (PSB) employing Pikovskaya (PK) medium with tricalcium phosphate and 16S rRNA gene sequencing. From a total of 157 isolates that showed a halo zone on PK plates, three representative isolates (one from each location) were selected based on their population dominance and halo zone size for genetic identification using 16SrRNA sequencing. Interestingly, the isolated PSBs from the three sites showed highly similar nucleotide sequences with Acinetobacter baumannii, which were reported in the Philippines as multi-drug-resistant disease-causing microorganisms. However, in this present report, the A. baumannii isolates were characterized to have the ability to solubilize Phosphorus; with the Mindoro Occidental isolate (MOc PSB-RGL-2023) possessing 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 A. baumanii as bioinoculant for improving P availability in the soil thus, provides a valuable insight as the pioneer report that isolated and characterized A. baumannii-similar isolates from the three provinces in the Philippines as a prospective PSB bioinoculant.