CaCO3 and SrCO3 bioprecipitation by fungi isolated from calcareous soil

The urease-positive fungi Pestalotiopsis sp. and Myrothecium gramineum, isolated from calcareous soil, were examined for their properties of CaCO3 and SrCO3 biomineralization. After incubation in media amended with urea and CaCl2 and/or SrCl2, calcite (CaCO3), strontianite (SrCO3), vaterite in different forms [CaCO3, (CaxSr1-x)CO3] and olekminskite [Sr(Sr,Ca)(CO3)(2)] were precipitated, and fungal 'footprints' were observed on mineral surfaces. The amorphous precipitate mediated by Pestalotiopsis sp. grown with urea and equivalent concentrations of CaCl2 and SrCl2 was identified as hydrated Ca and Sr carbonates by Fourier transform infrared spectroscopy. Liquid media experiments showed M.gramineum possessed the highest Sr2+ removal ability, and similar to 49% of supplied Sr2+ was removed from solution when grown in media amended with urea and 50 mM SrCl2. Furthermore, this organism could also precipitate 56% of the available Ca2+ and 28% of the Sr2+ in the form of CaCO3, SrCO3 and (CaxSr1-x)CO3 when incubated in urea-amended media and equivalent CaCl2 and SrCl2 concentrations. This is the first report of biomineralization of olekminskite and coprecipitation of Sr into vaterite mediated by fungi. These findings suggest that urease-positive fungi could play an important role in the environmental fate, bioremediation or biorecovery of Sr or other metals and radionuclides that form insoluble carbonates.