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. In this dataset Escherichia coli and Bacillus subtilis cultures were labeled with different percentages of single-carbon 13C glucose (13C2). Cultures of B. subtilis and E. coli were grown in Bacillus minimal medium or M9 minimal medium (E. coli) in which a percentage of the glucose was replaced with 13C2 glucose for >10 generations to achieve close to complete labeling of cells. The following percentages of 13C2 glucose were added 0, 0.01, 0.025, 0.1, 0.25, 1, 5 and 10%. Triplicate cultures were grown for each percentage. Please note that the unlabeled glucose that was used of course had a natural content of 13C of around 1.1%, thus the 0% added label samples have an actual 13C content of 1.1% 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.