Growth Phase-Dependent Antioxidant Enzyme Defense of Humicola lutea against Copper Stress

Copper is an essential element for the growth and development of the full range of living organisms, including filamentous fungi. At the same time, it is toxic for organisms when present in excess. The present study was conducted to assess the role of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) on the tolerance strategy of the fungal strain Humicola lutea 103 at different growth phases under enhanced Cu ions concentrations. We examined the changes in the growth, intracellular protein content and levels of antioxidant enzyme defense. The results revealed that the presence of Cu ions affected the duration of growth phases in a dose-dependent manner. The effect of Cu treatment (150 g/ml Cu ions) depends on the age of the treated culture. The spores and cells from the stationary growth phase demonstrated higher resistance compared to the corresponding control due to the enhancement of SOD and CAT activity. The increased total SOD activity was largely due to the Cu/Zn-SOD isoform. The non-growing cells taken from cultures of different growth phases demonstrated also up-regulation of both antioxidant enzymes in response to oxidative stress imposed by the ROS-generating heavy metal. During the stationary-phase, H. lutea cells demonstrated higher resistance to Cu-induced oxidative stress compared with the exponential phase cells.