The protons of gluconic acid are the major factor responsible for the dissolution of tricalcium phosphate by Burkholderia cepacia CC-Al74

Burkholderia cepacia CC-Al74 with a high ability for solubilizing tricalcium phosphate (TCP) was used to study the P-solubilization mechanism. We collected filtrates able to solubilize TCP from the cultures of strain CC-Al74 and demonstrated that the P-solubilization increased from 0 μg ml−1 to 200 μg ml−1 during exponential growth, when the pH decreased from 8 to 3. HPLC-analysis revealed that the solubilization of TCP was mainly caused by the release of 16.3 mM gluconic acid. At this concentration, gluconic acid was capable of solubilizing 376 μg ml−1 of TCP whereas water at pH 3 only solubilized 35 μg ml−1. The difference is due to the final H+ concentrations which were 13.5 mM and 1 mM in 16.3 mM gluconic acid and deionized water, respectively at pH 3.