Bacterial acid phosphatase and its application to waste remediation and metal recovery

Abstract

PhoN-type acid phosphatase from an atypical Serratia sp. was applied to the removal of radionuclides from aqueous flows. In the presence of metal ions the phosphatase produces metal phosphate at the cell surface via the liberation of inorganic phosphate from a phosphate donor (glycerol-2-phosphate). Previous studies using biogenic hydrogen uranyl phosphate (HUP) on Serratia sp. removed \(^{60}\)Co, \(^{137}\)Cs and \(^{90}\)Sr via intercalative ion exchange into the HUP crystal lattice. Due to their non toxic and non radioactive nature, zirconium phosphates offer an alternative to HUP for the decontamination of potable water. Zirconium was successfully biomineralised by Serratia sp. forming gel-like deposits with little or no crystalline phases, as shown by XRD. This biogenic zirconium phosphate removed 100 % Co\(^{2+}\) and Sr\(^{2+}\) from solutions. Increased capacity can be achieved by co-crystallisation with Zr(IV) supplement assuming phosphatase radioresistance.
The Serratia sp. phosphatase exists in two distinct isoforms (SP1 (radioresistant) and SP2 (radiosensitive)) which were purified and further characterised in this study. Both isoforms were found to have redox capability and were able to potentiate free radical damage to deoxyribose in a Fenton-type reaction. Analysis using highly sensitive Micro-Proton Induced X-ray Emission (PIXE) analysis found no metallic components in SP1 or SP2. Database interrogation using partial sequences of the phosphatase and the Basic Local Alignment Search Tool (BLAST) confirmed homology with PhoC and PhoN of several pathogenic bacterial species and also similarities with the vanadium haloperoxidases, indicating these phosphatases and peroxidases could have a common ancestor. The relatedness of the Serratia sp. PhoN to pathogenic species producing PhoN is discussed along with the possible role of phosphatase as both a scavenger of phosphate and in providing a defense mechanism for the pathogenic bacterial cell against the free radical-mediated immune response of the host.