Transformation of calcite (CaCO3) into earlandite [Ca3(C6H5O7)2·4H2O] by the fungus Trichoderma asperellum BDH65

Biotransformation of amorphous calcium carbonate into calcite and other inorganic calcium minerals is a worldwide phenomenon in the bacterial kingdom. In this study, it showed that calcite (CaCO3) could be transformed into an organic mineral earlandite [Ca3(C6H5O7)2·4H2O], through the dissolution of calcite and subsequent crystallization by the fungus Trichoderma asperellum BDH65. Observations by light microscopy showed that the fungal induced crystal particles were deposited as irregularly granular accumulations of micro globular particles. Scanning and transmission electron microscopy revealed that each micro globular particle consists of numerous needle-like crystals with domed end assembling radially with their ends pointing outside from its centers. This is clearly different from the shapes of microsheets formed by the chemical method. The mineral phase of the fungal catalyzed crystals is identified as earlandite, which is chemically identical to calcium citrate tetrahydrate. Structure and properties of the fungal formed crystals are further characterized by Fourier transform infrared spectroscopy and thermogravimetry, showing a similar pattern with those observed for chemically synthesized calcium citrate tetrahydrate. The current result may useful for understanding bioweathering of minerals and rocks, and insight into the calcium cycling driven by fungi. [Display omitted] •Transformation of calcite into earlandite by a fungus is demonstrated.•Fungal earlandite are characterized by XRD, SEM, TEM, FTIR and SAED.•The fungal particles are aggregated as irregular nodules consisting of spheroids.•The biogenic earlandite consist of needle-like crystals with domed end.