Characterization of rhizosphere products especially 2-ketogluconic acid

Examination of rhizosphere products of wheat seedlings using a variety of Chromatographie techniques established that 2-ketogluconic acid was the only acid present in significant amounts. Elemental analysis of crystallized potassium 2-ketogluconate isolated from the rhizosphere products and data obtained by X-ray diffraction, i.r. spectrometry and specific rotation determinations confirmed the identification of the 2-ketogluconic acid. Spectrophotometric and specific rotation measurements showed that 2-ketogluconic acid represented about 20% of the rhizosphere products. Furthermore, the 2-ketogluconic acid was present in fractions of rhizosphere products shown to release phosphate from calcium phosphates. Pure 2-ketogluconic acid released phosphate from apatite rock, di- and tri-calcium phosphates. In each case there was an associated decrease in pH of the suspensions compared with controls.About 38% of the rhizosphere products was carbohydrate, and glucose and fructose were the dominant free sugars present. Since 2-ketogluconic acid is known to be a product of microbial action on glucose and the organisms involved occur in the rhizosphere it is likely that the 2-ketogluconic acid was produced from glucose in the rhizosphere.