Investigating the Metabolic Versatility Toward Inorganic Phosphorus of a Promoting Growth Plant Rhizobacteria Isolated from Phosphate Mine Area

Phosphate deposits is a special environment, characterized by high stringent conditions. Bacterial community associated with this ecotype has been extensively studied in the context of soil fertilization and improvement of agricultural yields. However, little is known about their ability to promote mineral formation through bio-accumulation or bio-precipitation although the presence of multiple evidences about their role in the construction of these geological formations. All these facts suggest that microbial population inhabiting this environment could display at least one of these abilities: to solubilize, precipitate or accumulate phosphorus. Soil sample was taken from a rhizosphere of autochthonous plant growing spontaneously in a phosphate mine area situated in the region of Gafsa (Southern Tunisia) in order to isolate potential bacterial strains involved in these processes. Cultivation based techniques were used to isolate autochthonous bacterial strains. Simple qualitative tests were applied to screen phosphorus solubilization and phosphorus biomineralization abilities. Results revealed the presence of bacterial strain displaying the three aptitudes to solubilize, to accumulate and to precipitate phosphorus according to applied condition of culture. Phylogenetic analysis based on 16S rRNA gene homology of one of these bacterial strains revealed that the isolated bacterial strain belongs to the class of γ proteobacteria related to Acinetobacter group. Results speculates that medium alkalinization is the main process that drive phosphorus precipitation. These preliminary results highlight the metabolic redundancy of Acinetobacter toward phosphorus element an emphasis its pivotal role in phosphorus cycling. These exploratory results suggest the usefulness of this bacterium for phosphorus removal and recovery purposes in addition to its potential contribution as plant promoting growth bacterium for soil fertilization. Orientation to metabolic pathway seems to be dictated by extracellular environmental conditions.