An investigation on tolerance and biosorption potential of Aspergillus awamori ZU JQ 965830.1 TO Cd(II)

The minimum inhibitory concentration (MIC) value of Aspergillus awamori for Cd(II) was 700 mg/l. A complete inhibition of biomass production was observed at 400 mg/l concentration of Cd(II). A significant deformation in Cd(II)-stressed conidiophores and conidia was observed by Scanning electron microscopy (SEM) investigation. Quantification of Cd(II) was performed by EDX microanalysis. Transmission electron microscopy investigation (TEM) confirmed the involvement of extracellular adsorption, intracellular penetration through the cell wall and vacuolation. Cadmium(II) stress induced noticeable changes in the activities of polyphenol oxidase (PPO), glutathione reductase (GR) and peroxidase (POD), and in the concentrations of total antioxidants, soluble protein and thiols. High performance liquid chromatography analysis (HPLC) revealed that Cd(II) stress stimulated the production of oxalic acid. Maximum Cd(II) uptake capacity was achieved at pH 5.0, initial metal ion concentration 500 mg/l and biomass dosage 1 g/l. Maximum Cd(II) uptake capacity was reached after 6 h for live biomass and after 2 h for dead biomass. Fourier transform infrared spectroscopy (FTIR) results gave an indication on chelation between oxygen-, nitrogen-, phosphorus- and especially sulphur-containing ligands of biomass with metal ions. X-ray diffraction analysis (XRD) revealed the presence of CdSO4 (H2O)-H-. by live and dead biomass. EDX confirmed the occurrence of sulphur, oxygen and Cd(II) on the cell wall.