Abstract

The Bacillus by their intrinsic properties have several mechanisms of procuring beneficial effects to plants. They are among the most successful bacterial communities in the solubilization of phosphates. Ten Bacillus strains were isolated from the rhizosphere of wheat from three areas in arid and semi-arid regions in Algeria. These strains were tested for their ability to solubilize phosphates on liquid and solid media: LB (Luria-Bertani), NBRIP (National Botanical Research Institute Phosphate) and PVK (Pikovskaya) supplemented with Ca₃(PO₄)₂ (5 g/l). The highest levels of soluble phosphates were obtained on PVK and NBRIP liquid (177.68 and 173.28 µg/ml for D13 and D1 strains, respectively). Phosphates solubilization is always associated with a decrease in the pH of the medium. An inverse relationship (r = -0.4224) existed between the levels of soluble phosphate and the decrease of pH in medium. To test the solubilization capacity of theBacillus strains under salt stress, concentrations of NaCl (0, 2, 4, 6 and 8%) were added to the NBRIP medium. The solubilization capacity was negatively affected by the increase of salinity. However, the response of the Bacillus to salt was strain dependent. Strains D1 and D13, which produced the best rate of solubilization were used to study the ability of osmoprotectants (glycine-betaine, proline) to restore the ability to solubilize phosphate at high salt concentrations. However, these strains do not seem to accumulate these types of osmoprotectants.

Key words: Bacillus, phosphate solubilization, NaCl, osmoprotectant.