Microbial formation of crystalline strontium carbonate

Pseudomonas fluorescens appeared to grow in a mineral medium containing strontium (5 mM) complexed to citrate, the sole source of carbon, without any evident inhibition in cellular yield. Atomic absorption studies showed that the divalent metal was excluded from the cytoplasmic component and was initially found in the supernatant fluid in soluble form(s). However, as growth progressed, strontium was immobilized as a light green extracellular residue. X-ray fluorescence spectroscopy, X-ray diffraction spectrometry, Fourier transform infrared spectroscopy and acid treatment revealed that this insoluble moiety was crystalline strontium carbonate. Scanning electron microscopy aided in the identification of rounded bodies associated with these strontium carbonate crystals. A three-fold increment in the level of dissolved carbon dioxide observed in the spent fluid from the strontium supplemented medium would imply that this moiety may be playing a pivotal role in the deposition of the mineral.