Halotolerant phosphate solubilizing bacteria isolated from arid area in Tunisia improve P status and photosynthetic activity of cultivated barley under P shortage

Forty-seven (47) bacterial strains were isolated from soil of Gabes (an arid region in southern Tunisia) and were screened for their ability to produce Indole-3-Acetic Acid (IAA) and to solubilize phosphate (P). The characterization and molecular identification of the most successful P-solubilizing bacteria (PSB) were then carried out. When grown on suitable artificial media, the most salt-tolerant strains also showed the highest P solubilization capacity (up to 126.8 μg ml^-1 of released phosphorus after 7 day incubation) and the strongest ability to produce IAA (up to 101.86 μg ml^-1 after 3 day incubation). Overall, bacterial isolates displayed a different tolerance to varying pH, temperatures, and salinity. The molecular identification revealed that 11 strains belonged to three genera: <i>Bacillus</i>, <i>Pseudomonas</i> and <i>Mesorhizobium</i>. Inoculation of barley with P-solubilizing bacteria under tricalcium phosphate-induced P shortage significantly improved plant growth (biomass, shoot height, and root length) together with increasing total chlorophyll contents and photosynthetic activity. This was concomitant with (i) higher P uptake and translocation and (ii) increased phosphorus absorption and utilization efficiencies (PAE and PUE), which is indicative of a better plant P nutrition under P scarcity. Taken together, we provide strong arguments showing that bacteria native to extreme environments display PSB potential making them promising candidates to mitigate low Pi availability for crop plants.