Biomineralization of Metal Carbonates by Neurospora crassa

In this research, the urease-positive fungus Neurospora crassa was investigated for the biomineralization of calcium carbonate and its potential application in metal biorecovery and/or bioremediation. After 12 d incubation at 25 °C in urea and calcium-containing medium, extensive biomineralization of fungal filaments was observed. Energy dispersive X-ray analysis of crystalline precipitates on the hyphae of N. crassa showed that the main elements present in the crystals were Ca, C, and O. X-ray diffraction (XRD) of the precipitates showed they were composed solely of calcite (CaCO3) and over 90% Ca could be removed from the media by the fungal biomass and associated calcite precipitation. To further investigate biologically induced metal carbonate biomineralization, CdCl2 was contacted with supernatants of N. crassa obtained after growth in urea-containing medium. XRD showed that the Cd2+ was precipitated as pure otavite (CdCO3) with a particle size range of 55 to 870 nm, and approximately 1.5% having nanoscale dimensions. These results provide direct experimental evidence for the precipitation of metal carbonates such as calcite and otavite based on biologically induced mineralization, and suggest that urease-positive fungi may play a potential role in the synthesis of novel biominerals and in metal bioremediation or biorecovery.