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.
Highlights
Improving soil fertility is one of the most common strategies to increase agricultural production
The results of the efficiency of phosphate solubilization of Bacillus strains differed depending on the media (Figure 1)
The results showed that the acidification of Pikovskaya medium (PVK) and National Botanical Research Institute Phosphate (NBRIP) media was significantly the same and played a role in the mechanism of phosphate solubilization
Summary
Improving soil fertility is one of the most common strategies to increase agricultural production. Chemical fertilizers are the main strategy for the availability of phosphorus in agricultural soils, but about 75 to 90% of phosphate fertilizers added are precipitated by iron, aluminium and calcium complexes present in soils (Gyaneshwar et al, 2002; Turan et al, 2006). With high levels of exchangeable calcium, soluble phosphate reacts with CaCO3, precipitates and forms minerals of insoluble Ca-P (Lindsay et al, 1989). The accumulation of this form is a crucial problem in agriculture. The use of rhizospheric microorganisms is the best biological means to enhance solubilisation of phosphate in the soil and to provide sufficient quantities for plant nutrition (Pradhan and Sukla, 2005; Singh et al, 2011). The ability of some microorganisms to convert the insoluble phosphate to an accessible form is an important trait for plant growth promoting rhizobacteria (PGPR) to Cherif-Silini et al
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