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 Cd(2+) 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.

The fungi Aureobasidium pullulans , Mortierella humilis , Trichoderma harzianum and Phoma glomerata were used to investigate the formation of selenium- and tellurium-containing nanoparticles during growth on selenium- and tellurium-containing media. Most organisms were able to grow on both selenium- and tellurium-containing media at concentrations of 1 mM resulting in extensive precipitation of elemental selenium and tellurium on fungal surfaces as observed by the red and black colour changes. Red or black deposits were confirmed as elemental selenium and tellurium, respectively. Selenium oxide and tellurium oxide were also found after growth of Trichoderma harzianum with 1 mM selenite and tellurite as well as the formation of elemental selenium and tellurium. The hyphal matrix provided nucleation sites for metalloid deposition with extracellular protein and extracellular polymeric substances localizing the resultant Se or Te nanoparticles. These findings are relevant to remedial treatments for selenium and tellurium and to novel approaches for selenium and tellurium biorecovery.

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 , (Cax Sr1-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 Sr(2+) removal ability, and ∼ 49% of supplied Sr(2+) 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 Ca(2+) and 28% of the Sr(2+) in the form of CaCO3 , SrCO3 and (Cax Sr1-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.

No abstract

Electrical energy storage systems such as rechargeable lithium-ion batteries (LiBs) and supercapacitors have shown great promise as sustainable energy storage systems [1-4]. However, LiBs have high specific energy density (energy stored per unit mass) and act as slow, steady suppliers for large energy demands. In contrast, supercapacitors possess high specific power (energy transferred per unit mass per unit time) and can charge and discharge quickly for low energy demands. In LiBs, graphite is the most common anode material, although high electrolyte sensitivity and low charge capacity can limit performance. Efforts have been made to improve LiB or supercapacitor performance using alternative electrode materials such as carbon nanotubes and manganese oxides (MnxOy) [3, 5-14]. Microorganisms play significant roles in metal and mineral biotransformations [15-22]. Fungi possess various biomineralization properties, as well as a filamentous mycelium, which may provide mechanical support for mineral deposition. Although some research has been carried out on the application of biological materials as carbon precursors [8, 9, 23], biomineralizing fungal systems have not been investigated. In this research, novel electrochemical materials have been synthesized using a fungal Mn biomineralization process based on urease-mediated Mn carbonate bioprecipitation [24]. The carbonized fungal biomass-mineral composite (MycMnOx/C) showed a high specific capacitance (>350 F g(-1)) in a supercapacitor and excellent cycling stability (>90% capacity was retained after 200 cycles) in LiBs. This is the first demonstration of the synthesis of electrode materials using a fungal biomineralization process, thus providing a novel strategy for the preparation of sustainable electrochemical materials.