Isolation and In Vitro Potential Test of Phosphate Solubilizing Bacteria from Asiatic Pennywort (Centella asiatica L. Urban) Rhizosphere

Abstract

<em>Asiatic pennywort (Centella asiatica), a potential medicinal plant, is widely grown in the highlands dominated by Andisols. Phosphorus deficiency is one of the most common cultivation constraints in Andisols soils. Applying phosphate-solubilizing bacteria is an alternative to overcome P nutrient deficiency in Andisol soil because it can dissolve insoluble phosphate into soluble phosphate and produce growth hormones for plants. The study aimed to obtain phosphate-solubilizing bacteria isolates from the Asiatic pennywort rhizosphere, which can also produce IAA hormones and phosphatase enzymes. Bacteria were isolated on Pikovskaya medium, which was specific as phosphate solvent. Parameters observed were phosphate solubilization index, gram stain test, colony morphology, phosphatase activity, and indole acetic acid (IAA) production. Based on the isolation result, 29 isolates were Gram-negative bacteria, and one was Gram-positive. Twenty-five bacterial isolates could dissolve P; 10 isolates had the highest P solubilization index, possessed phosphatase activity, and produced IAA. The phosphatase activity ranged from 2.153–2.272 µg.g<sup>-1</sup>.hour<sup>-1,</sup> and IAA production was between 3.668–7.385 ppm. Three bacterial isolates from the Asiatic <em>Pennyworth rhizosphere LMP 3.11, LMP 1.11, and LMP 3.18 showed the ability to dissolve phosphate in vitro of 5.04-7.00 µg.g<sup>-1</sup>.hour<sup>-1</sup> and generated IAA 6.611-7.385 ppm. However, the three isolated bacteria are still required to evaluate for their safety in plants (hypersensitivity test) and mammals (hemolysis test). Furthermore, they should be formulated and tested for potency on Asiatic pennyworth grown on Andisols.</em></em>