Submitted to: World Congress of Soil Science
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/2002
Publication Date: N/A
Technical Abstract: A phosphate-solubilizing bacterium Enterobacter intermedium, isolated from rhizosphere, exhibited a strong ability to solubilize insoluble phosphate. This ability was mediated by the production of organic acids in culture media. The organic acids produced by E. intermedium were identified using a high performance liquid chromatography and a gas chromatograph mass spectrometer. 2-ketogluconic acid (2-KGA) was identified as the main organic acid released by E. intermedium. This bacterium oxidized glucose to gluconic acid and sequentially converted it into 2-KGA. The ability of E. intermedium to solubilize phosphate and 2-KGA production in broth medium containing different components was monitored under aerobic and anaerobic conditions. Soluble phosphate and 2-KGA concentrations gradually increased, whereas pH in culture media decreased throughout the incubation period under both aerobic and anaerobic conditions. Under aerobic condition, the production of 2-KGA markedly increased to about 110 g/L at 10 days in GGR (glucose 0.6M, gluconic acid 0.2M and rock phosphate 5%) and GGRC media (glucose 0.6M, gluconic acid 0.2M, rock phosphate 5% and CaCO3 1%), while the concentration of soluble phosphate significantly increased to about 1000 mg/L in GR (glucose 0.8M and rock phosphate 5%) and GGR media. In GRC (glucose 0.8M and rock phosphate 5% and CaCO3 1%) media, the concentrations of 2-KGA and soluble phosphate were about 60 g/L and 250 mg/L, respectively. When E. intermedium was grown in broth culture medium under aerobic conditions, the pH of the medium was negatively correlated with phosphate concentration, which indicated that the solubility of phosphate and decreased pH were due to the production of organic acids. Under anaerobic condition, the concentration of 2-KGA was about 5.5 g/L in all treatments. Phosphate concentration was about 40 mg/L when E. intermedium was grown in GR and GGR media, whereas it was only 10 mg/L in GRC and GGRC media. Our results indicate that culture medium should be supplemented with gluconic acid as an initiator, CaCO3 as a buffer agent, and O2 as a terminal electron acceptor for optimum production of 2-KGA by E. intermedium. However, for phosphate solubilization, CaCO3 should be omitted from culture medium.