Fig. 4. Molecular methods to study microbiome-host interfaces from DNA and RNA-based approaches, to emergent metaproteomics and metabolomics in order to evaluate microbial gene expression, taxonomic profiles, and deeper-level genomes. Newer approaches include both mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectrometry, which are the most used non-sequencing-based methods for molecular-level investigation of the human gut microbiome. Source: Adapted from Ilhan (2016).