Zinc Oxalate Crystal Formation by<i>Aspergillus nomius</i>

Abstract

This research investigated the ability of an Aspergillus species, isolated from zinc-containing mineral ore, for its ability to transform insoluble zinc oxide (ZnO). It was plated on potato dextrose agar (PDA) medium supplemented with 0.5% (w/v) zinc oxide. Mycogenic crystals were observed under colonies grown in zinc oxide-amended plates. These crystals were investigated by scanning electron microscopy (SEM) and X-ray powder diffraction (XRPD) and identified as zinc oxalate. When compared with zinc oxalate produced by an abiotic reaction, it was found that the crystals were different in their morphology. The production of organic acids in the culture medium was analyzed by high performance liquid chromatography (HPLC). Organic acids are known to be directly involved in metal transformations, especially oxalic acid which plays an important role in metal mobilization and immobilization processes. Increasing heavy metal concentrations in the culture medium caused a significant decrease in the biomass yield. The Aspergillus was identified as Aspergillus nomius, which has not been previously reported regarding heavy metal compound transformation ability.