Isolation and Identification of the High Efficient Phosphate-solubilizing Bacteria from the Rhizosphere of Brassica chinensis L. and the Optimization of Culture Conditions

In order to evaluate the ability of microorganism in the rhizosphere of Brassica chinensis L. to decompose the organic phosphorus, the taxonomic status of its dominant phosphate-solubilizing bacteria was clarified, and the culture conditions were further optimized, thus to provide the basis for the development of microbial fertilizers. The organic phosphorus-decomposing bacteria in the rhizosphere of Brassica chinensis L. were screened by using the Mengjinna organic phosphorus plate method, and the phosphate-solubilizing ability of the strains was analyzed through the molybdenum antimony resistance colorimetric method. Then, the colonial morphology of the dominant phosphate-solubilizing bacteria was further observed. And the phylogenetic tree was constructed through the homology comparison of 16S DNA sequence and nearest neighbor method to determine the taxonomic status of the dominant strain FG5. Last, the optimum culture conditions of strain FG5 were further explored by using the single factor and orthogonal experiments. The results showed that: three strains of organic phosphate-solubilizing bacteria were isolated and screened from the rhizosphere of Brassica chinensis L., among which the strain FG5 had the best phosphate-solubilizing effect. After the inoculation with strain FG5 and culture for 3 days, the mass concentration of free phosphorus in the medium was as high as 165.20 ug·mL^-1. The colony of FG5 was circular with a dry surface and slight protrusions, and the edges were wavy off white. The homology comparison results of the 16S DNA sequence indicated that the strain FG5 was Bacillus tequilensis. The results of single factor and orthogonal experiments showed that the optimum culture conditions for the strain FG5 were as follows: mannitol as carbon source, urea as nitrogen source, culture temperature of 27℃, rotational speed of 180 r·min^-1, inoculation amount of 1.5% (V/V). Under this condition, the phosphate-solubilizing ability of FG5 reached 307.25 ug·mL^-1, which was 85.99% higher than that before the optimization of culture conditions. The strain FG5 had a strong ability to decompose the organic phosphorus and had good potential for the application of microbial fertilizers.