The peroxidase activity of all micromycetes cultivated in the medium containing 0.005 M NiCl₂ was low and manifested only in the later period of growth. Th e highest peroxidase activity was observed in Aspergillus repens (1.56 au/ml). In the medium with the concentration of 0.01 M NiCl₂ no peroxidase activity was found, except Mortierella verticillata in which the maximum (3.97 au/ml) was reached on the 4th day of cultivation.

The concentration of 0.005 M NiCl₂ stimulated the tyrosinase activity of all micromycetes studied. The highest tyrosinase activity was observed in Myrothecium verrucaria, Sporotrichum pruinosum, Galactomyces geotrichum and Oedocephalum albidum (59.2–121.5 cu/ml) in the whole period of growth. The major concentration (0.01 M) of NiCl₂ stimulated the tyrosinase activity in all micromycetes. Th e infl uence of 0.01 M of NiCl₂ increased the enzymatic activity of all micromycetes 3.74 to 141.8 times in comparison with the control. During the whole period of cultivation, the highest enzymatic activity was observed in Oedocephalum albidum, and its maximum was reached (357.28 cu/ml) on the 18th day of cultivation.

The highest laccase activity in the medium containing 0.005 M NiCl₂ was observed after 21 days of cultivation (it increased 1.3 to 3.3 times in comparison with the control). The major concentration (0.01 M) of NiCl₂ decreased the laccase activity in all micromycetes, except Galactomyces geotrichum in which the enzymatic activity on the 18th day of cultivation increased 1.5 times in comparison with the control.

Keywords: nickel, micromycetes, peroxidase, laccase, tyrosinase