Adaptive response to oxidative stress in the filamentous fungus Aspergillus niger B1-D

In the present study, we used a recombinant filamentous fungus strain, Aspergillus niger B1-D, as a model system, and investigated the antioxidant defences in this organism. Our findings indicate that pretreatment with low concentrations of H 2O 2 completely prevents killing by this oxidant at high concentrations. It shows that A. niger adapts to exposure to H 2O 2 by reducing growth and inducing a number of antioxidant enzyme activities, including superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, of which the induction of catalase is the most pronounced. Moreover the decline of these antioxidant enzymes activities after H 2O 2 detoxification, coincides with recommencement of growth. Results from monitoring the extracellular H 2O 2 concentration clearly indicate a very rapid detoxification rate for H 2O 2 in adapted A. niger cultures. A mathematical model predicts only very low concentrations of intracellular H 2O 2 accumulating in such cultures. Our results also show that glutathione plays a role in the oxidative defence against H 2O 2 in A. niger. On addition of H 2O 2, the intracellular pool of glutathione increases while the redox state of glutathione becomes more oxidized.