PubMed · 13098578
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1953-08-29. PHOSPHATE cycle.. https://pubmed.ncbi.nlm.nih.gov/13098578/
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Phosphorus is an essential element for plant growth. However, in nature, most phosphorus exists in the form of insoluble compounds that plants cannot directly absorb, leading to phosphorus deficiency in agricultural systems. With increasing demand for economic crops such as citrus and the decline in soil fertility due to current management practices, there is a growing need for environmentally friendly fertilizers to improve and restore soil conditions. In this study, a highly efficient phosphate‑solubilizing strain X32 was isolated from the rhizosphere soil of Gannan navel oranges. Systematic genomic analysis identified it as a putative novel species within the genus Bacillus, showing the closest phylogenetic relationship to Bacillus spizizenii. However, both the average nucleotide identity (ANI = 93.18%) and digital DNA‑DNA hybridization (dDDH = 50.4%) values fell below the established thresholds for species delineation, indicating significant genomic differentiation. Whole‑genome sequencing further revealed that strain X32 harbors multiple functional genes potentially related to phosphorus metabolism, including inorganic phosphate‑solubilizing genes (e.g., gdh and gltA), phosphate transport genes (e.g., glpT, pstA, pstB, pstC), and phosphorus mineralization genes (e.g., phoA, phoD). Pot experiment results demonstrated that inoculation with strain X32 significantly promoted the growth of navel orange seedlings, as evidenced by marked increases in both aboveground and belowground fresh and dry weights, as well as plant height. Additionally, strain X32 significantly enhanced the activities of antioxidant enzymes (SOD, CAT, POD) and regulated the content of chlorophyll b in seedling leaves, these changes suggest that strain X32 may enhance stress resistance in plants and influence photosynthetic pigment composition, though direct measurements of photosynthetic performance are needed for confirmation. This study provides a theoretical basis for developing microbial fertilizers with efficient phosphorus solubilization and plant growth-promoting functions, which may help reduce dependence on phosphorus fertilizers and promote sustainable agricultural development.
The polarities of the co-existing phases of a polyethylene glycol (PEG)-2000-K3PO4 aqueous biphasic system (ABS) have been examined using Reichardt's carboxylated pyridinium-N-phenoxybetaine dye as a probe. Using this probe, the polarities of these phases have been compared to those of conventional solvent extraction systems and micellar systems using values obtained from the literature. In general, these extraction systems are comparable in polarity to rather polar solvents. Data on the free energy of transfer of solvents suggests that this may be due to the failure of the probe to account for the real polarity of the salt-rich phase compared to the polymer-rich phase. Examination of the monophasic region of these systems suggests that the reason for this is that the probe is partitioned to a discreet solvent domain dominated by PEG, even though phase separation of the solution is not observed. The use of linear free energy relationships for the characterization of ABS is briefly discussed.
A spectrophotometric method for inorganic phosphate determination in the presence of thiol compounds is described. Thiol compounds, which interfere with the measurement of inorganic phosphate by a modification of the method of Gomori, are removed by carboxymethylation by iodoacetate prior to the formation and reduction of phosphomolybdate complex. A linear standard curve is obtained by this method, and the method is suitable for the assay of a phosphate-releasing enzyme when the measurement must be performed in the presence of thiol compounds.