Ky. Kim et al., SOLUBILIZATION OF HYDROXYAPATITE BY ENTEROBACTER-AGGLOMERANS AND CLONED ESCHERICHIA-COLI IN CULTURE-MEDIUM, Biology and fertility of soils, 24(4), 1997, pp. 347-352
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.