Location of hot spring FS5 in YNP. Microscopy image of unsorted hot spring cells visualized with general nucleic acid stain, 4′,6-diamidino-2-phenylindole (DAPI). Scale bar represents 5 µm. Samples were incubated in the presence of L-homopropargylglycine (HPG) under various treatments (Supplementary Table 1) for 48 h. Cells were detached from particle material and newly synthesized proteins were dye-stained via azide-alkyne click chemistry. Translationally active, fluorescent cells were sorted using fluorescence-activated cell sorting (FACS) from the presort, total extractable cell community. Cells were lysed and 16S rRNA genes were amplified with PCR. Black squares (■) in cells represent new proteins containing HPG. Map of YNP provided by the US National Park Service. Satellite image obtained from Google Maps.