Abstract: Several strains of phosphate-solubilizing bacteria were isolated and screened from the crop rhizosphere of calcareous soil in Shanxi Province of China. After repeated isolation and purification, the strain W25 with strong phosphate-solubilizing activity was obtained, and identified as Rahnella sp., based on the morphological, physiological and biochemical properties and the analysis of 16S rRNA gene sequence. Further studies on the W25 showed that the maximum phosphate solubilizing capability of the W25 on tricalium phosphate, aluminum phosphate and ferric phosphate reached 385.5, 110.4 and 216.6 mg·L^-1, respectively. In the liquid culture with aluminum phosphate and ferric phosphate, the solubilized phosphorous by the W25 was significantly negatively correlated with the liquid pH, with the correlation coefficient being 0.56 and 0.81, respectively. Among the carbon and nitrogen sources, glucose and ammonium nitrate were the optimum for the solubilization of tricalium phosphate by W25. The utilization of carbon source was in the order of glucose > lactose > sucrose > mannitose > starch, and that of nitrogen source was in the order of ammonium nitrate > ammonium chloride > ammonium sulfate > potassium nitrate > sodium nitrate. Different nitrogen sources had greater effects on the production of organic acids by W25. Formic acid and acetic acid would be produced when the nitrogen source was NH₄⁺, oxalic acid and succinic acid would be produced when the nitrogen source was NO₃^-, and citric acid would be extra produced when the ammonium nitrate was used as the nitrogen source.

Key words: calcareous soil, Rahnella sp.,  , phosphate-solubilizing characteristics.