Merging isotopes and community genomics in a siliceous sinter-depositing hot spring.

Thermophilic microbes in hydrothermal ecosystems have multiple metabolic strategies for taking up carbon and nitrogen, which may result in distinct stable isotopic compositions of C and N in living biomass, as well as other biosignatures that accumulate in the geologic record. Biofilms from "Bison Pool" at Yellowstone National Park display large variations in carbon and nitrogen isotopic values as a function of downstream sampling and illustrate the presence of large shifts in ecological functions as temperature decreases. This is the first study to couple isotopic data with community genomic analysis to predict dominant carbon fixation pathways that create hydrothermal biofilm signatures. The results also suggest nitrogen limitation through the chemotrophic zone and nitrogen fixation in the lower-temperature phototrophic zone.