Diversity and activity of phosphate bioleaching bacteria from a high-phosphorus iron ore

Many of the current world iron ore resources contain over 0.08 w% of P, making this material out-of-standard for the manufacture of metallic iron and steel. Solubilization of phosphatic minerals can be performed by some bacteria, which in turn become useful in developing environmental friendly solutions for various human activities, such as agriculture and mining. When artificially inoculated in a particular environment, indigenous microorganisms, as a general rule, compete better in terms of adaptation and cause fewer ecological distortions than exogenous microorganisms. In this way, the aims of this study were to isolate and characterize phosphate-solubilizing bacteria associated to a high-phosphorous iron ore located in the Brazilian region of Minas Gerais and to determine the mechanisms by which they solubilize phosphorous moieties. Phosphorus content of the ore material is 0.18% (w:w) and, therefore, it is considered as a high-phosphorus iron ore. Among the culturable bacteria associated to the iron ore, four morphologically distinct bacterial strains showed high phosphate-solubilizing activity. They were identified by 16S rRNA gene sequencing as four different species: Leifsonia xyli FeGl 02, Burkholderia cenocepacia FeSu 01, Burkholderia caribensis FeGl 03 and Burkholderia ferrariae FeGl 01. In addition to tricalcium phosphate [Ca3(PO4)2] solubilization activity, the two later strains were also tested for solubilization of berlinite [AlPO4] and turquoise [CuAl6(PO4)4(OH)8·5H2O] in plate culture. Although both strains were able to growth in the berlinite-amended medium, none showed solubilizing activity. Neither B. caribensis FeGl 03 nor B. ferrariae FeGl 01 grew in the turquoise-amended medium. The rates of P solubilization and production of gluconic acid, 2-ketogluconic acid, acetic acid and citric acid were assayed in flask-shake cultures growing in a medium supplemented with hydroxyapatite [Ca5(PO4)3(OH)]. There was no appreciable difference in the rate of P solubilization between these two strains. Although neither 2-ketogluconic nor citric acid were detected in the broth media, both strains produced gluconic acid and acetic acid. However, a remarkable difference in the evolution of the gluconic acid concentration was observed between B. caribensis FeGl 03 and B. ferrariae FeGl 01.