Characterization of Phosphate-Solubilizing Pseudomonas lurida OR400772, and Potential Application in Tricalcium Phosphate Contaminated Soil to Alter Vicia faba Growth, and Gene Expression Patterns

Abstract

Phosphorus (P) fertilizers augment agricultural production despite their adverse environmental impacts, as they deplete plants of P through frequent soil P fixation. Therefore, this study investigated and characterized the potential alternative, phosphate-solubilizing Pseudomonas lurida (Pl) "OR400772" from the alfalfa rhizosphere. The in vitro characterization of P solubilizing activity on Pikovskaya’s (PVK) media, in addition to other plant growth-promoting activities of Pl strain, was investigated. The in vivo validation of Pl strain in a pot experiment for Vicia faba L. growth in tricalcium phosphate (TCP)- containing soil was evaluated. The HPLC analysis demonstrated that the synthesis of citric acid and gluconic acid promotes the solubilization of phosphorus by Pl, consequently lowering the media's pH to 3.2. Furthermore, Pl strain was able to produce ammonia, indole acetic acid (IAA), and hydrogen cyanide (HCN). Pl-inoculated V. faba plants growing in TCP-containing soil exhibited a significant increase in plant biomass, with particularly notable increase in root development i.e. root dry weight was 10.3 times larger, and exhibited higher rhizosphere colonization index. The total soluble protein rose significantly by 83.86 % compared to the control, with reduced free amino acids and enhanced photosynthetic pigments. The gene expression profiles of ribulose-bisphosphate carboxylase oxygenase (rbcl), plasma membrane H+-ATPase (PM-H+-ATPase), and calcium-dependent protein kinase (CDPK5); key genes of metabolic pathways related to photosynthesis, nutrient uptake, and signaling mechanisms, suggesting molecular mechanisms underlying the observed growth promotion. This study showed that P. lurida may be a better biofertilizer than synthetic compounds in agricultural systems. This may help preserve soil fertility and the environment.