Updated project metadata. This dataset is part of a study aimed at developing algorithms for the quantification of stable isotope content in microorganisms after labeling them with stable isotope-labeled substrates. For this dataset Escherichia coli cultures were labeled with 2.5 % of 15N-labeled NH4Cl and grown either anaerobically or aerobically. Cultures of E. coli were grown in M9 minimal medium in which 2.5 % of the ammonium was replaced with 15N-labeled NH4Cl for >10 generations to achieve close to complete labeling of cells. Triplicate cultures were grown. Please note that the unlabeled ammonium that was used of course had a natural content of 15N of around 0.4 %, thus the 0% added label samples have an actual 15N content of 0.4 % and all added label is on top of this value. We included a tab delimited table with this submission providing details on all raw files.