Low oxygen conditions are not only common to natural environments but also occur during tissue invasive growth in the human host. Only few cellular factors have been identified up to now that allow the fungus to efficiently adapt its energy metabolism to the lack of O2. In the present study, we cultivated A. fumigatus in an O2-controlled fermenter and analysed its minute-scale responses to O2 limitation. Transcriptome sequencing revealed a group of genes underlying a rapid and highly dynamic regulation. As an initial experimental setup, A. fumigatus was cultivated in an O2-controlled fermenter, which allowed minute-scale variations in O2-fluxes largely independent of other secondary effects. Cultures were initially grown at saturated O2 concentrations (100% saturation ˜ 260 µmol l-1) and rapidly shifted to hypoxic growth conditions at an initial O2 saturation of 5% (˜ 13 µmol l-1). Overall design: Dynamics of low and high O2 responses of A. fumigatus cultivated in an O2-controlled fermenter