Isolation and characterization of mineral phosphate-solubilizing bacteria naturally colonizing a limonitic crust in the south-eastern Venezuelan region

摘要

With the aim to explore the possible role of mineral phosphate-solubilizing bacteria (PSB) in phosphorus (P) cycling in iron-rich, acidicsoils, we conducted a survey of PSB naturally colonizing a limonitic crust in the south-east region of Venezuela (Bolívar State). A total of130 heterotrophic bacterial isolates showing different degrees of mineral tri-calcium phosphate (Ca3(PO4)2)-solubilizing activities wereisolated from NBRIP plates. In contrast, no isolates showing iron phosphate (FePO4)- or aluminum phosphate (AlPO4)-solubilizingactivities were detected by this experimental approach. The 10 best Ca3(PO4)2-solubilizers were selected for further characterization.These isolates were shown to belong to the genera Burkholderia, Serratia, Ralstonia and Pantoea by partial sequencing analysis of theirrespective 16S rRNA genes. All the PSB isolates were able to mediate almost complete solubilization of Ca3(PO4)2 in liquid cultures; incontrast, the PSB isolates were less effective when solubilizing FePO4. Two groups of PSB isolates were clearly differentiated on the basisof their Ca3(PO4)2 solubilization kinetics. Acidi.cation of culture supernatants seemed to be the main mechanism for P solubilization.Indeed, gluconic acid was shown to be present in the supernatant of .ve isolates. Furthermore, detection of genes involved in theproduction of this organic acid was possible in three isolates by means of a PCR protocol.