Phosphate Solubilization and Organic Acids Production by Enterobacter sp. 15S Isolated from Horticultural Soil in Londrina, Brazi

Introduction: Deficiency of phosphorus in soils is one of the most important chemical factors restricting plant growth. Through the releasing of organic acids into the soil, phosphate solubilizing bacteria are capable to provide this element to plants. Hence, the present study aimed to study the ability of Enterobacter sp. 15S, a bacterial strain originally isolated from soil under conventional horticultural management, in solubilize tricalcium phosphate and produce organic acids. Methods: The phosphate solubilization ability of Enterobacter sp. 15S was evaluated using the liquid NBRIP medium supplemented with 1 g of Ca3(PO4)2 as source of phosphorus per L and initial pH adjusted to 6.8. The experiments were carried out in 1 L Erlenmeyer flasks containing 300 mL of NBRIP medium in triplicate each treatment. The bacterium was inoculated at final concentration of 106 cells mL-1 and the flasks were incubated at 28 °C with shaking at 180 rpm for 7 days. A non-inoculated flask was used as control. Aliquots of bacterial culture were collected at initial time (before inoculation) and at every 24 h after inoculation, following centrifugation (5,000 g, 5 min) and elimination of any bacterial cells from the supernatant by sequential filtration through Whatman filter paper followed by 0.22 µm Millipore filter. Filtered supernatant was used to determine pH and concentrations of soluble phosphate and organic acids. Results: The soluble phosphate increased from 0.10 mM to 14.88 mM as the pH decreased from 6.8 to 4.4 along experimental period, in the flasks inoculated with the Enterobacter sp. 15S. Five different organic acids were detected from the culture medium in which Enterobacter sp. 15S was growing, including one unknown peak (10.8 min). Out of the five different organic acids, α-ketoglutaric acid was produced in largest quantity (11.9 mM), followed by malic acid (7.30 mM), oxalic acid (2.01 mM), citric acid (1.13 mM) and fumaric acid (0.55 mM). Conclusions: Since in this study it was possible to verify the phosphate solubilizing and acid organic production ability by the Enterobacter sp. strain 15S, its use as inoculant could increase the available P content in soils and at least partially substitute chemical P-fertilizer application. Funding Agencies: Capes, CNPq, Fundação Araucária, UEL.