Characteristics of the Phosphorus-Solubilizing Bacteria Derived from the Rhizosphere of Persimmon Tree in Beijing and their Plant Growth-Promoting Potential

In this study, fourteen active phosphorus solubilizing bacteria (PSB) were obtained by qualitative and quantitative experiments from the rhizosphere of persimmon grown in Beijing, China, with a relatively dry climate. Based on the 16S rRNA gene sequencing, the PSB isolates were clustered under two phyla with Proteobacteria (accounting for 64.28%) and Firmicutes (35.72%). The former included four genera, Pseudomonas (28.57%), Phyllobacterium (21.43%), Variovorax (7.14%), and Mesorhizobium (7.14%), while Bacillus (21.43%) and Paenibacillus (14.29%) belonged to Firmicutes. These PSB strains showed different degrees of phosphate solubilization capacity from 8.36 to 226.28 mg/L in the fermentation culture. Further, the plant growth-promoting potentials include indol-3-acetic acid (IAA), siderophores, and proteases. Among them, eleven PSB strains produced IAA, ten strains had proteolytic activity, and four can produce siderophores. Significantly, this study was the first report of the PSB derived from the rhizosphere of persimmon trees, and the new functions of some isolates were detected as follows, V. soli SHI05 and M. helmanticense SHI08 can simultaneously produce IAA, siderophores, and proteases, P. knackmussii SHI01 and P. sophorae SHI12 can produce IAA, P. frederiksbergensis SHI02, P. illinoisensis SHI09, and P. illinoisensis SHI13 can secrete proteases, P. sophorae SHI03 can produce siderophores. The effect of bacterial inoculation on the early growth of mung bean revealed that V. soil SHI05 can distinctly improve the seed vigor index, total length, fresh weight, dry weight, and root activity of mung bean, increasing by 28.65, 28.71, 174.14, 237.56, and 9.39%, respectively, compared to the positive control (Bacillus megaterium). This showed that the rhizosphere of the persimmon tree was rich in diverse and multifunctional PSB, and V. soli SHI05 may have great potential to become a high-quality candidate microbial fertilizer agent in promoting the growth of mung bean.