Abstract: With the increasing use of chemical fertilizer, problems such as soil hardening and water pollution become more and more serious. In order to invent a new type of fertilizer to replace chemical fertilizer, 27 bacterial strains were screened from environment by inorganic-phosphorus solid medium. Mo-Sb colorimetry was used to evaluate the phosphorus-solubilizing capacity of 27 bacterial strains, and strain qzr14 had the highest capacity of phosphorus-solubilizing(270 mg/L). The growth-promoting effect of 27 bacterial strains were studied by pot experiments, qzr14 showed higher capacity on growth-promoting effect than others, increasing the height, dry weight and fresh weight of cucumber seedlings 27.7%, 98.4% and 57.0% than CK, respectively. The real-time monitoring organic acids in medium inoculated with qzr14 indicated that this strain mainly secreted gluconic acid to solubilize phosphorus. According to the analysis of phosphorus fractions in the soil of pot experiment, available P accounted 19.62%-22.57% of total P in the soil after 4 days treated by qzr14, while 12.53%-17.35% in the soil of CK, thus qzr14 solubilized insoluble-phosphorous in the soil. The results of biochemical testing demonstrated that qzr14 had the capacity of K-solubilizing and N-fixing；qzr14 was identified as Gluconacetobacter sp. by 16s rDNA analysis. In this article, Gluconacetobacter sp. qzr14 that may efficiently solubilize phosphorus is screened from the environment, and its growth-promoting mechanism is firstly reported. qzr14 solubilizes phosphorus in the soil by secreting gluconic acid, consequently more organic phosphorus is supplied to cucumber seedlings and therefore their growth is promoted. Also it probably has the ability of K-solubilizing and N-fixing to promote the growth of cucumber seedlings, conclusively this strain would be a potential microbial fertilizer.

Key words: screening of strain, efficient phosphorus-solubilizing bacteria, mechanism of plant-growth-promoting