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.