Abstract
Soil salinity is a significant constraint on agricultural productivity and disturbs the availability of nutritional elements necessary for plants, such as phosphorus. Microorganisms have specialized adaptation features, such as tolerance to salt, stimulation of growth, and the ability to promote plant survival under saline conditions. The objectives of this investigation were to isolate new salt-tolerant, phosphate-solubilizing bacterial strains, assess their phosphate-solubilizing activity, and investigate the mechanisms of phosphate mobilization under salinity stress. Phosphate-solubilizing bacteria were isolated from saline pasture soils in southeastern Kazakhstan, and their salt tolerance and phosphate-solubilizing activity were identified. Three highly active strains were selected and identified by Sanger-based molecular genetic analysis: Enterobacter cloacae FY3, Pseudomonas putida FT4, and Bacillus megaterium F7A. Organic acid production by these strains under salt stress was analyzed using gas chromatography. The results indicated that the strains produced 12 organic acids, with differences in composition and amount between strains. The most important phosphate solubilization mechanism under salinity stress is the secretion of organic acids. Organic acid secretion, pH reduction, and increased soluble phosphorus content were positively correlated. These findings provide an effective method for phosphorus mobilization in salt soils, and the recovered strains are likely candidates for making biofertilizers applicable to salt environments. These new strains are candidates for the development of biofertilizers for saline soils.