Solubilization of phosphate by the Bacillus under salt stress and in the presence of osmoprotectant compounds

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 Ca 3 (PO 4 ) 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 the Bacillus 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.

Actinomycete Strains Isolated from Saline Soils: Plant-Growth-Promoting Traits and Inoculation Effects on Solanum lycopersicum

“…To assess the strains' ability to dissolve inorganic phosphate, 5 mm agar plugs of each actinomycete strains (collected from cultivated plates of ISP2 media kept at 30 • C for 7 days) were placed in plates with three different media containing Ca 3 (PO 4 ) 2 as the only source of phosphate: NBRIP (National Botanical Research Institute's Growth Medium) [26], PVK (Pikovskaya) [27], and LB (Luria Bertani) modified by glucose addition. The solubilization ability was estimated by measuring the transparent area formed around the colony after 7 days of incubation at 30 • C. The diameter of the solubilization halo for each isolate was determined by subtracting colony diameter from the total one (diameter of the halo -diameter of the colony) [28].…”

“…Spore suspension of each strain (100 µL) was inoculated in 10 mL of liquid PVK medium and incubated at 30 • C for 7 days in a rotary shaker at 150 rpm. After incubation, the cultures were centrifuged at 3000 rpm for 20 min [28], and the solubilized phosphorus was quantified in the supernatant by the colorimetric method of Olsen and Sommers [29].…”

Isolation, Identification, and Characterization of Phosphate-Solubilizing Bacteria from Tunisian Soils

“…These results are in accordance with the results of Nautiyal et al [ 39 ], who classified the liquid NBRIP medium as the best medium for testing the phosphate solubilization. Cherif et al [ 40 ] and Chibani et al [ 41 ] also reported that NBRIP is the preferred liquid medium for phosphate solubilization by the majority of rhizobacteria.…”