Impact of copper and its nanoparticles on growth, ultrastructure, and laccase production of Aspergillus niger using corn cobs wastes

Abstract

The influence of copper and its nanoparticles was studied relative to growth and ultrastructure of Aspergillus niger. Laccase production by A. niger using corn cobs as substrate at different concentrations of CuSO4 and copper nanoparticles (CuNPs) is reported. Fungus growth was induced at 100 ppm of CuNPs and CuSO4, while at 300 ppm, the growth inhibition was 65.6% and 86.9%, respectively. Fungus sporulation was reduced to 30.4% and 47.6% at 300 ppm of CuNPs and CuSO4, respectively, compared to the control (100%). Transmission electron microscopy revealed that CuSO4 and CuNPs treatments encouraged the deformed appearance of the fungus at 200 ppm and 300 ppm, particularly CuNPs. The CuNPs and CuSO4 induced laccase production at 1.67 U/mL and 1.51 U/mL at optimum concentrations 0.15 mM and 0.25 mM, respectively. The optimum concentrations of CuNPs and CuSO4 led to reduced incubation periods of 12 d and 14 d, respectively, required to produce the highest amount of laccase (1.66 U/mL and 1.53 U/mL), while without treatments, the incubation period increased to 16 d required for the highest amount of laccase production (1.36 U/mL). Induction of laccase production at acidic pH and at 30 °C was recorded with the addition of CuSO4 and CuNPs, while its effects were slight at pH above 6.