Isolation and characterization of phosphate-solubilizing bacteria from betel nut (Areca catechu) and their effects on plant growth and phosphorus mobilization in tropical soils

Phosphate-solubilizing bacteria (PSB) were isolated and characterized from the rhizosphere and bulk soils of Areca catechu plants. A long history of phosphate fertilizer use has elicited a direct effect on the incidence of soil PSB. Their abundance and ability to solubilize insoluble phosphate were significantly greater (P < 0.0001) in soils with low available phosphorus (P) content than in other soil types. Three efficient PSB strains, namely, ASL12, ASG34, and ADH302, were identified as Acinetobacter pittii, Escherichia coli, and Enterobacter cloacae by characterizing 16S rRNA sequences and biochemical characteristics; they produced gluconic acid at concentrations of 7862.4, 4306.5, and 2663.8 mg L−1, respectively. The highest amount of solubilized P was determined in Pikovskaya (PVK) medium for the bacterial strain ASL12. The secretion of gluconic acid was related to the available P of rhizosphere soils and P solubilization. Under shaded conditions, the application of these three strains significantly improved plant height, shoot and root dry weight, and nutrient uptake of A. catechu seedlings. A further increase in P solubilization was observed by co-inoculating the three strains and also applying tricalcium phosphate (TCP) or aluminum phosphate (AP). A significant (P < 0.05) correlation was also observed between P-solubilization activity and A. catechu plant growth in pot experiments. Thus, the three strains can be potentially applied as inoculants in tropical and aluminum-rich soils.