Hydroxyapatite Biosynthesis by a<i>Serratia</i>sp. and Application of Nanoscale Bio-HA in the Recovery of Strontium and Europium

Abstract

A Serratia sp. expresses a high level of acid phosphatase when grown continuously under carbon limitation. In the presence of CaCl 2 , biosynthesis of nanocrystalline hydroxyapatite (bio-HA) was achieved by utilizing phosphate released via enzymatic cleavage of an applied substrate (glycerol 2-phosphate: G2P). Hydroxyapatite crystals were identified by energy dispersive X-ray emission (EDX) and selected area diffraction (SAD). X-ray powder diffraction (XRD) analysis gave a mean crystallite size of 21-32 nm, with the smallest crystals (21-24 nm) obtained using 1 mM Ca 2C and 1 mM G2P. The uptake of Eu 3C and Sr 2C by bio-HA made by continuously pregrown cells (0.42 mg/mg and 0.043 mg/mg respectively) was 20% greater for Sr 2C than was previously reported for bio-HA material of size 40 nm made by batchpregrown cells, while the corresponding uptake of Eu 3C was increased by > 1.8-fold. This was attributed to the localization of Eu (III) at grain boundaries by reference to previous work and highlights the potential of bio-HA as a sequestration agent for recovery of rare earth elements and trivalent actinides.