Comparative analysis of microbial diversity across temperature gradients in hot springs from Yellowstone and Iceland

Geothermal hot springs are a natural setting to study microbial adaptation to a wide range of temperatures reaching up to boiling. Temperature gradients lead to distinct microbial communities that inhabit their optimum niches. We sampled three distant but chemically similar hot springs in Yellowstone and Iceland that had outflows and presented a wide range of temperatures. The microbial composition at different niches was determined by deep DNA sequencing of rRNA gene amplicons. Over three dozen phyla of Archaea and Bacteria were identified, representing over 1700 unique organisms. We observed a significant reduction in the number of microbial taxa as the temperature increased from warm (38{degrees}C) to boiling. The community structure was primarily driven by temperature and, at high taxonomic levels, was similar between Yellowstone and Iceland, suggesting that the environment rather than biogeographic location play the largest role in the microbial ecology of hot springs. We observed significant endemism at genus level, especially in thermophilic phototrophs, potentially driven by distinct environmental conditions and dispersal limitations.