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Lett Appl Microbiol. 2009 Aug;49(2):222-8. doi: 10.1111/j.1472-765X.2009.02642.x. Epub 2009 May 22.

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

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1
Department of Life Science and Environmental Biochemistry, Pusan National University, Miryang, Korea.

Abstract

AIMS:

To investigate the mechanism of insoluble phosphate (P) solubilization and plant growth-promoting activity by Pseudomonas fluorescens RAF15.

METHODS AND RESULTS:

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.

CONCLUSION:

This study indicated that the P solubility was directly correlated with the organic acids produced.

SIGNIFICANCE AND IMPACT OF THE STUDY:

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.

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