A Bacterium Isolated From Soil in a Karst Rocky Desertification Region Has Efficient Phosphate-Solubilizing and Plant Growth-Promoting Ability

Phosphorus in the soil accessible to plants can easily be combined with calcium ion, the content of which is high in karst rocky desertification (KRD) regions, thereby resulting in a low utilization efficiency of phosphorus. The application of phosphate-solubilizing bacteria (PSB) from the KRD region would facilitate enhanced phosphate availability in the soil. In the present study, the strains belonging to Acinetobacter, Paraburkholderia, and Pseudomonas with efficient phosphate-solubilizing ability were isolated from fruit tree rhizosphere soils in KRD regions. Particularly, Acinetobacter sp. Ac-14 had a sustained and stable phosphate-solubilizing ability (439-448 mg/L, 48-120 h). Calcium carbonate decreased the phosphate-solubilizing ability in liquid medium; however, it did not affect the solubilization index in agar-solidified medium. When cocultivated with Arabidopsis thaliana seedling, Ac-14 increased the number of lateral roots, fresh weight, and chlorophyll content of the seedlings. Metabolomics analysis revealed that Ac-14 could produce 23 types of organic acids, majorly including gluconic acid and D-(-)-quinic acid. Expression of Ac-14 glucose dehydrogenase gene (gcd) conferred Pseudomonas sp. Ps-12 with a sustained and stable phosphate-solubilizing ability, suggesting that the production of gluconic acid is an important mechanism that confers phosphate solubilization in bacteria. Moreover, Ac-14 could also produce indole acetic acid and ammonia. Collectively, the isolated Ac-14 from KRD regions possess an efficient phosphate-solubilizing ability and plant growth-promoting effect which could be exploited for enhancing phosphorus availability in KRD regions. This study holds significance for the improvement of soil fertility and agricultural sustainable development in phosphorus-deficient KRD regions.