| Summary: | 碩士 === 國立中興大學 === 分子生物研究所 === 85 === The purpose of this investigation is to explore the mineral
phosphate-solubilizing (MPS) mechanism of the phophate-
solubilizing Rhizobia. Two Rhizobia strains, B2 and B28, with
higher MPS activities were isolated from soybean nodules and
used in this study. In addition, the MPS activities of two
phosphate-solubilizing bacteria, Rhizobium fredii SB651 and
Bacillus pumillus Ca49-4, from Dr. C. C. Yang''s laboratory were
also analyzed. The results indicated that phosphate-solubilizing
bacteria decrease the pH valueof medium by secreting organic
acids. These organic acids include tartaric acid, citric acid,
oxalic acid, acetic acid, succinic acid and gluconic acid.The
MPS activities of phosphate-solubilizing bacteria were affected
by theamount and types of the organic acid secreted by the
bacteria. The results revealed that citric acid and oxalic acid
which containing cation chelator show better phosphate-
solubilizing activities . This was supported by the founding
that mutant strains of B2, B2-100-5 and B2-50-5, decreased the
citric acid and oxalic acid production and at the same time lost
the MPS activities.The result suggested that citric acid
production has a strong relationship with MPS activity of the
phosphate-solubilizing bacteria. The citrate synthase gene
(ccsA) of Rhizobium tropici was amplified by polymerase chain
reaction with two designed primers, ccsA-F2 and ccsA-B2. The 1.3
kb PCR product was subsequently cloned into pSK- and pKS-
vectors and transformed to E. coli. The amplified ccsA gene was
further identified by partial DNA sequence analysis. Two
proteins with molecular weight of 47 kDa and 52 kDa were
observed by maxicell analysis. These two proteins represent the
originaland fusion citrate synthase of R. tropici, respectively.
However, no significant increase in the amount of citric acid
production by the transformed E. coli strain was found.
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