Isolation and Identification of Phosphate Solubilizing Bacillus spp. from Tamarix ramosissima Rhizosphere and Their Effect on Growth of Phaseolus vulgaris Under Salinity Stress

The use of rhizobacteria associated with plant roots in extreme environments could be a promising strategy to overcome the limitations of crop production induced by soil salinity. In the present study, we isolated phosphate solubilizing bacteria from the rhizosphere of Tamarix ramosissima which is common native plants grown on a saline-alkaline site, to investigate the ability of these bacteria to alleviate salt stress in common bean (Phaseolus vulgaris cv. Karnac) plants. Among 5 isolates could solubilize phosphate, we selected the two most efficiency isolates No. 4 (AL-18) and No. 2 (AL-19). The partial sequence of 16S rDNA genes and phylogenetic tree indicated that AL-18 and AL-19 related to Bacillus megaterium and Bacillus cereus respectively. B. megaterium AL-18 and B. cereus AL-19 could survive and solubilize inorganic phosphate up to 14% NaCl. Maximum solubilization of tri-calcium phosphate (TCP) by both strains was observed at 6% NaCl and pH 7. The effect of selected strains on common bean growth under salt stress was conducted in pots experiments under greenhouse condition. Growth parameters including root length, plant height, root and shoot dry weight, phosphate content in plants and photosynthetic pigments were significantly increased by single and dual inoculation of the two selected strains under salt stress conditions. In conclusion, our results showed that inoculation of Phaseolus vulgaris with B. megaterium AL-18, B. cereus AL-19 isolated from the rhizosphere of Tamarix ramosissima, can alleviate the deleterious effects of salinity and improve plant growth, phosphate uptake and photosynthetic pigments under salt stress conditions, which were demonstrated in vivo. However, field experiments under natural conditions are needed to study the mechanisms by which the identified strains induce salinity tolerance in plants.