Phosphate solubilizing bacteria associated with the rhizosphere of sandalwood (Santalum album L.) and their phosphate solubilizing ability

Some soil microorganisms living around plant roots are essential in supplying plant nutrients. According to preliminary studies, phosphate solubilizing bacteria have the ability to convert insoluble phosphates into a soluble form that it is available to plants. Therefore, this study was carried out to examine the activity of phosphate solubilizing bacteria that inhabit the rhizosphere of sandalwood (Santalum album L.) plants in solubilizing inorganic phosphate (tricalcium phosphate (Ca₃ (PO₄)₂), aluminium phosphate (AlPO₄), and iron phosphate (FePO₄)) as sole P sources with organic phosphate (p-nitrophenyl phosphate disodium and sodium phytate) as the substrate. A total of 16 isolates of phosphate solubilizing bacteria (PSB) were selected based on the formation and dimensions of the halo zone around the colony. All the isolates were able to solubilize the three different inorganic phosphates in culture broth and mineralize the organic ones, such as Acid, Alkaline and phytase. Isolates P4 and P5, which had the highest phosphate solubilization potential, were selected and identified by sequencing the 16S rRNA genes. The results showed that they were related to Priestia megaterium strain P4 and Priestia megaterium strain P11, respectively. The maximum solubility of inorganic P was 150.28 µg/ mL (Ca₃(PO₄)₂, 109,13 µg/ mL (FePO₄), and 21.25 µg/ mL (AlPO₄). Meanwhile, the solubility of organic P was recorded to be 127.57 U/ mL (acid phosphatase), 152.42 U/ mL (alkaline phosphatase), and 4.17 U/ mL (phytase). Optimum conditions found were temperature at 30-35 °C, pH 7.0 and in the presence of lactose and dextrose as carbon sources and peptone and Ammonium chloride as nitrogen for P4 and P11 respectively The potential bacteria obtained can be developed as microbial inoculants for various soil types, such as acidic or alkaline soil.