we conducted a large-scale comparison of high-temperature hot springs from YNP, Iceland, and Japan, sampled at sites where temperature and geochemical conditions preclude photosynthesis, because non-photosynthetic populations (i.e., those dependent on chemotrophy) should more closely reflect geochemical differences among hot springs. Sediment and water samples from hot springs were subjected to molecular microbiological and aqueous geochemical analyses to identify potential geologic and geochemical differences associated with host springs and how such differences may shape the composition of microbial communities.