Avaliação da capacidade de solubilização de fosfato orgânico por acidobacteria AB23 e AB60

Abstract

Phosphorus is the second most important macronutrient for plants, being associated with several biological processes, but its availability in soluble form in the soil is reduced due to its great capacity to chelate other minerals. A sustainable way to provide soluble phosphorus to plants is through phosphate-solubilizing microorganisms, which possess mechanisms that transform insoluble phosphorus, such as the release of phosphatase enzymes. These enzymes have a subgroup called phytases, which perform the solubilization process using phytate as a substrate, a form of organic phosphorus widely present in the soil. Acidobacteria is a recently discovered phylum, present in large quantities in Cerrado soils, and the hypothesis of this work is that the AB23 and AB60 strains, isolated from these soils, participate in phosphorus cycling through phytate solubilization by the release of phytases. For this purpose, the strains were cultivated in standard VL-55 culture medium, phosphorus-free medium, and medium containing phytate as a phosphorus source, using serial dilutions for statistical analyses of bacterial growth by colonyforming unit counts. During the work, modifications were made to the experiment to improve the results obtained. Additionally, both strains were also cultivated in modified Pikovskaya medium containing phytate, in order to evaluate the presence of phytases through the formation of a solubilization halo. After cultivation and growth for 4 weeks at 28°C under the presence of light, following the changes made to the methodology, strain AB23 showed growth up to 10⁻⁸ in the standard medium, 10⁻⁶ in the modified medium, and 10⁻⁸ in the negative control, with subsequent cell death. Strain AB60 showed growth up to dilution 10⁻⁷ in the positive control, 10⁻⁴ in the modified medium, and 10⁻⁵ in the negative control. Statistical analyses showed that both strains had statistically lower growth than their positive controls, but AB23 had higher growth than the phosphorus-free medium, while AB60 had statistically equivalent growth. Neither strain showed growth in Pikovskaya medium at any of the phytate concentrations. The present study demonstrated the need for further future experiments to confirm the results regarding strain AB60, and that AB23 has the capacity to solubilize organic phosphorus in the form of phytate, indicating its participation in phosphorus cycling in Cerrado soils and its potential use as a bioinput to make phosphorus available to plants.