Functional analysis of pqqE and GDH genes in Pseudomonas fluorescens CLW17 strain

Abstract:

[Background] Phosphorus is a macronutrient for plant growth, but most of it cannot be absorbed by plants. Phosphate-solubilizing microorganism (PSM) can secrete organic acids to dissolve the insoluble soil phosphates, improve plant growth, crop yield and quality by increasing phosphorus utilization.[Objective] The research aims to study the physiological functions of pqqE and GDH genes in the Pseudomonas fluorescens CLW17 strain. [Methods] Bioinformatics analyses have been done for two gene encoding proteins using bioinformatics software. We obtain two deletion mutant strains (CLW17ΔpqqE and CLW17ΔGDH) of pqqE and GDH gene by homologous recombination technology, and the corresponding supplementary strains (ΔpqqE/pqqE and ΔGDH/GDH) were obtained using the combined transfer method. The phosphate solubilizing abilities and organic acid production abilities of wild-type, mutant strains, and complementary strains were detected by NBRIP medium, molybdenum anti colorimetry method, and high-pressure liquid chromatography (HPLC) method, respectively. [Results] The numbers of amino acids encoded by pqqE and GDH genes were 390 and 803, respectively. There is no signal peptide for both genes. pqqE had no transmembrane domain, while GDH predicted five transmembrane domains. The pqqE and GDH genes are the phosphate-solubilizing genes of the CLW17 strain, and the deletion of the two genes greatly reduces the phosphate-solubilizing ability of this strain, moreover, the complementary strains of these two genes can restore the phosphate-solubilizing ability. Wild strain CLW17 can secrete a variety of organic acids, among which gluconic acid content is the highest, followed by acetic acid. The ability to produce organic acids in the knocked-out strain was greatly reduced, especially the ability to produce gluconic acid and acetic acid. [Conclusion] The pqqE and GDH genes are the key genes for the phosphate solubilization of the CLW17 strain, the phosphate solubilization ability of the strain is closely related to the production of organic acids, especially gluconic acid and acetic acid. This study laid the foundation for further study on the interaction and phosphorus solubilization mechanism between the strain and Taxus chinensis var. mairei.