A method of isotope-labelling a microbiota sample. It involves providing a first microbiota sample that was obtained from a given source; exposing the first microbiota sample to an isotope enriched medium; and culturing the exposed first microbiota sample in the isotope enriched medium to obtain an isotope-labelled microbiota sample, wherein the isotope labelled metaproteome of the isotope-labelled microbiota sample is taxon specific for taxa present in the first microbiota sample when initially obtained from the given source.