Updated publication reference for PubMed record(s): 29844191. We developed a method that allows measuring the stable carbon isotope composition of individual species in microbial communities using metaproteomics. We call this methods “Direct Protein-SIF”. To benchmark this method, we measured twenty pure culture species using the Direct Protein-SIF method as well as Isotope Ratio Mass Spectrometry. Some of the pure cultures were measured in technical replicates to see how consistent Protein-SIF measurements are between mass spec runs. This submission thus contains 29 raw files for the pure cultures. See table in the submission for details of which species was measured for which .raw file. We also included the Direct Protein-SIF specific isotope pattern files as well as the .mzML files and PSM files required as input for the Direct Protein-SIF software. In addition to the pure culture a protein reference material (MKH files) was measured. The respective .raw files and isotopic pattern files are also included in this submission (see publication for details on how the reference material is used to calibrate the method).