Objective To isolate and screen phosphorus-solubilizing bacteria from the soil of Chinese fir (Cunninghamia lanceolata) plantation in red soil region and optimize its culture conditions.

Method The phosphorus-solubilizing bacteria were isolated and screened by Pikovskava (PVK) medium. The strains with strong phosphorus-solubilizing capacity were identified by physiological and biochemical tests and 16SrDNA gene sequence alignment. Single factor test was used to compare the phosphorus-solubilizing capacity of the strains under different culture time, initial pH, culture temperature, inoculum size, carbon source, nitrogen source and phosphorus source. Orthogonal test was used to optimize the culture conditions of the strains.

Result Thirteen strains were screened out, among which the phosphorus-solubilizing capacity of strain P5 was the highest. The content of available phosphorus of strain P5 in PVK was 196.61 mg·L⁻¹. Strain P5 were identified as Burkholderia ubonensis by physiological and biochemical tests and sequence analysis of 16SrDNA gene. Single factor test showed that strain P5 was resistant to high temperature and low pH. The result of the orthogonal experiment indicated that the optimal culture condition of strain P5 are as follows: 2.0% (w/v) sucrose, 0.2% (w/v) ammonium chloride, pH 5.5, 30℃, under which the maximum phosphorus-solubilizing capacity could be up to 268.69 mg·L⁻¹ and the content of available phosphorus was about 40% higher.

Conclusion The result indicates that strain P5, a highly efficient phosphorus-solubilizing bacteria, could be a potential candidate for the development of microbial fertilizer applied to environmentally stressed soil due to their phosphorus-solubilizing capacity and tolerance to high temperature and low pH.