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Mechanism of insoluble phosphate solubilization by Pseudomonas fluorescens RAF15 isolated from ginseng rhizosphere and its plant growth-promoting activities

Park, K.-H., Lee, C.-Y., Son, H.-J.
Letters in applied microbiology 2009 v.49 no.2 pp. 222-228
Panax, Pseudomonas fluorescens, acetic acids, biofertilizers, biological control agents, excretion, fructose, gluconic acid, glucose, growth promotion, high performance liquid chromatography, hydrogen cyanide, indole acetic acid, nitrogen, pH, phosphates, plant growth, polygalacturonase, proteinases, rhizosphere, siderophores, solubility, solubilization
To investigate the mechanism of insoluble phosphate (P) solubilization and plant growth-promoting activity by Pseudomonas fluorescens RAF15. We investigated the ability of Ps. fluorescens RAF15 to solubilize insoluble P via two possible mechanisms: proton excretion by ammonium assimilation and organic acid production. There were no clear differences in pH and P solubilization between glucose-ammonium and glucose-nitrate media. P solubilization was significantly promoted with glucose compared to fructose. Regardless of nitrogen sources used, Ps. fluorescens RAF15 solubilized little insoluble P with fructose. High performance liquid chromatography analysis showed that Ps. fluorescens RAF15 produced mainly gluconic and tartaric acids with small amounts of 2-ketogluconic, formic and acetic acids. During the culture, the pH was reduced with increase in gluconic acid concentration and was inversely correlated with soluble P concentration. Ps. fluorescens RAF1 showed the properties related to plant growth promotion: pectinase, protease, lipase, siderophore, hydrogen cyanide, and indoleacetic acid. This study indicated that the P solubility was directly correlated with the organic acids produced. Pseudomonas fluorescens RAF15 possessed different traits related to plant growth promotion. Therefore, Ps. fluorescens RAF15 could be a potential candidate for the development of biofertilizer or biocontrol agent.