SOLUBILIZATION OF HYDROXYAPATITE BY ENTEROBACTER-AGGLOMERANS AND CLONED ESCHERICHIA-COLI IN CULTURE-MEDIUM

Phosphate-solubilizing bacteria (PSB) possessing the ability to solubi lize insoluble inorganic phosphate were isolated from the rhizosphere soil of wheat. A laboratory study was conducted to investigate the sol ubilization of phosphate by a known PSB, Enterobacter agglomerans, and by a genetically manipulated bacterium, Escherichia coli. A second la boratory study investigated the release of P from E. agglomerans compa red with known acids. For the first laboratory study, a cosmid (pHC79) library of phosphate-solubilizing gene(s) from E. agglomerans chromos ome DNA was constructed in E. coli JM109. The clone JM109 (pKKY) showi ng phosphate solubilization properties was screened on standard medium containing hydroxyapatite (HY). The P concentration significantly inc reased at 5 and 10 days for JM109 (pKKY) compared with JM109 (pHC79), the control. Although the P concentration increased, there was no sign ificant change in their pHs. Furthermore, an increase in colony-formin g units (CFUs) was seen at 5 and 10 days for JM109 (pKKY) but not for JM109 (pHC79). Artificial acidification of the culture medium with HCl , citric acid, oxalic acid, and lactic acid was achieved by shaking fo r 48 h. Acidification with these selected acids solubilized more HY th an E. agglomerans growing for 42 h at similar pHs. However, a high P c oncentration was measured in culture medium with E. agglomerans growin g for 84 h despite similar pHs. Our results suggest that acid producti on may play an important role in HY solubilization, but is not the sol e reason for the increase in P concentration in culture medium.