Isolation and phosphorus-solubilizing mechanism of Achromobacter xylosoxidans in the rhizosphere of Moso bamboo

Abstract:

Objective To isolate the strain for solubilizing both inorganic and organic phosphorus (P) from the rhizosphere of Moso bamboo (Phyllostachys edulis) and mine the related genes, laying a foundation for activating the soil P pool and improving P bioavailability by P-solubilizing microorganisms (PSM).Methods High-throughput screening was employed to isolate PSM strains from the rhizosphere of Moso bamboo, an important economic plant in subtropical regions. The P-solubilizing activities of the strain under various carbon sources and soil P levels were investigated by microplate culture and soil inoculation experiments, respectively. The genes involved in P solubilizing of the strain were mined by whole-genome sequencing.Results The strain zafu-3 (Achromobacter xylosoxidans) capable of solubilizing P via multiple pathways was isolated from the rhizosphere of Moso bamboo. The strain solubilized Ca₃(PO₄)₂, FePO₄, AlPO₄, lecithin, and calcium phytate by using four carbon sources such as glucose and citric acid, with the highest P-solubilizing activity of 32.75 mg/(L·d). Compared with the control group, the zafu-3 inoculation group showed increases of 4.21%-33.88% and 13.54%-112.06% in activities of acid phosphatase and alkaline phosphatase, respectively. In the high P-level soil, inoculation of the strain decreased the soil pH by 0.04 and increased the available P content by 16.32%. The whole genome of strain zafu-3 contained 35 genes encoding phosphohydrolases and 53 genes involved in organic acid metabolisms. Furthermore, strain zafu-3 carried the genes associated with the production of indole-3-acetic acid and siderophores, and the degradation of lignin.Conclusion Strain zafu-3 directly solubilized inorganic and organic P by secreting diverse organic acids and phosphatases, and indirectly activated soil P pools by promoting plant growth. These findings provide an important microbial resource and theoretical foundation for the development of multifunctional biofertilizers.