Metabolite profiles under cultivations of Aspergillus niger at three levels of pH. For each pH value is shown three replicates, from which biomass was sampled for transcriptome analysis. Sample times are shown with white vertical lines. Note that the pH shown in the left column is the pH at the time of sampling for transcriptome analysis. All cultures were inoculated at pH 2.5 and increased at the beginning of the growth phase if needed (see Methods for details).