Rahnella aquatilis, a bacterium isolated from soybean rhizosphere, can solubilize hydroxyapatite

A diazotropic bacterium, ISL19, has been isolated from soybean rhizosphere. ISL19 grows well at 30 degrees C and utilizes diverse carbon sources for its growth. This Gram-negative bacterium is rod-shaped, is about 2-3 mu m in size and contains several flagella. On the basis of its cellular fatty acid profile, its carbon utilization pattern, and the nucleotide sequence of a conserved segment of a 16S rRNA gene, ISL19 has been identified as Rahnella aquatilis. This bacterium exhibited a strong ability to solubilize hydroxyapatite and dicalcium phosphate in the external culture medium. The solubilization of hydroxyapatite was associated with a drop in the pH of the culture medium. The change in the pH value showed an inverse correlation with the soluble phosphorus concentration. Analysis of the culture medium by high pressure liquid chromatography identified gluconic acid as the main organic acid released by R. aquatilis.