Submitted to: Journal of Microbiology and Biotechnology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/2003
Publication Date: 12/1/2003
Citation: Cho, Y., Park, R., Kim, Y., Hwangbo, H., Jung, W., Shu, J., Koo, B., Krishnan, H.B., Kim, K. 2003. Pqq-dependent organic acid production and effect on common bean growth by rhizobium tropici ciat 899. Journal of Microbiology and Biotechnology. 13:955-959. Interpretive Summary: Phosphorus, an essential mineral macronutrient, is required for maximum yield of agriculturally important crops. Soil contains only a small percentage of the total phosphorus in a soluble form. The rest is chemically bound in insoluble complexes (mineral phosphate). Farmers are thus asked to apply several-fold excess phosphorus fertilizers in order to overcome this problem. Rhizobium, a soil-dwelling bacterium, forms nodules on the roots of legume plants. The nodules are specialized structures where atmospheric nitrogen is fixed by the bacterium, which in turn, is utilized by legume plants for growth and development. This process is termed biological nitrogen fixation and it enables legumes, including soybeans to grow in nitrogen-poor soils. In this study, we have demonstrated that Rhizobium, in addition to providing the plants with reduced nitrogen, was also capable of solubilizing mineral phosphate into forms that can be utilized by plants for their growth and development. Information obtained from this basic study demonstrates that Rhizobium can be utilized as a potential biofertilizer. Farmers can benefit by reducing the use of expensive phosphorus fertilizers for promoting maximum yield of agriculturally important crops.
Technical Abstract: Rhizobium tropici CIAT 899 is capable of synthesizing inactive apo-glucose dehydrogenase (GDH). To become an active holo enzyme, GDH requires the cofactor pyrrolo quinoline quinone (PQQ). When R. tropici CIAT 899 was grown in a broth culture medium containing hydroxyapatite and PQQ, the pH decreased while the concentration of soluble phosphorous increased. The solubilization of hydroxyapatite was associated with the production of gluconic and 2-ketogluconic acids. The organic acid production and phosphate solubilization were much enhanced when the bacterium was grown with air supply. Effect of R. tropici CIAT 899 with (CI+PQQ) and without PQQ (CI) on the common bean growth was examined. Shoot and root weight, and N and P contents in the CI+PQQ treatment were significantly higher than those in the control and CI treatment. Nodule weight and acetylene reducing activities were also significantly higher in the CI+PQQ treatment than in other treatments.