Elevated temperature effects on the oxidant/antioxidant balance in submerged batch cultures of the filamentous fungus Aspergillus niger B1-D.

In the present study the relationship between oxidative stress and elevated culture temperature was examined in an industrially relevant fungal culture, Aspergillus niger B1-D. For the first time, both the intracellular levels of the main stressor species (superoxide radical [O(2) (.-)]) and activities of cellular defensive enzymes (superoxide dismutase [SOD], catalase [CAT], and glutathione peroxide [GPx]) were quantified at varying temperature (25, 30, 35, 40 degrees C) to more fully characterize culture response in different growth phases. Elevated culture temperature led to increased O(2) (.-) levels in various culture phases. In the exponential phase this was due to an enhanced generation of O(2) (.-), whereas in stationary phase a decreased dismutation rate may also have contributed. CAT activities generally increased with culture temperature, whereas GPx activity changed little as temperature rose, indicating that GPx played only a minor role in destroying H(2)O(2) in this A. niger. The combination of elevated temperature (35 degrees C) and increased O(2) supply (50% enrichment) led to decreased levels of O(2) (.-) compared to the cultivation at 35 degrees C gassed with air, probably due to enhanced activity of the alternative fungal respiratory pathway. Our findings indicate that while elevated cultivation temperature does clearly induce oxidative stress events, mechanistically, it does so by a rather more complex route than previous studies indicate. Elevated temperature caused a marked disparity in the activities of SOD and CAT, very distinct from the integrated increase in activity of these enzymes in response to oxidative stress.