Evidence for high‐temperature in situ nifH transcription in an alkaline hot spring of Lower Geyser Basin, Yellowstone National Park

Researchers have established a new upper temperature limit of 72.7°C for nitrogen fixation in alkaline, terrestrial hydrothermal environments, specifically within the Mound Spring outflow channel in Yellowstone National Park's Lower Geyser Basin. This discovery highlights the genetic capacity of microbes to fix nitrogen at high temperatures (57.2°C to 80.2°C), with evidence of active nifH gene expression up to 72.7°C, despite the absence of transcripts at higher temperatures (> 72.7°C). The study suggests that while microbes retain the genetic potential for nitrogen fixation, they may express it transiently or not at all under extreme conditions. Field measurements and stable isotope analysis further support these findings, indicating fixed nitrogen limitation as temperature decreases downstream. Additionally, the research identifies novel nifH sequences in both photosynthetic and chemosynthetic microbial communities, marking the first report of in situ nifH expression in strictly chemosynthetic zones of terrestrial hydrothermal systems.

Loiacono, S. T., Meyer‐Dombard, D. R., Havig, J. R., Poret‐Peterson, A. T., Hartnett, H. E., & Shock, E. L. (2012). Evidence for high‐temperature in situ nifH transcription in an alkaline hot spring of Lower Geyser Basin, Yellowstone National Park. Environmental Microbiology, 14(5), 1272–1283. Portico. https://doi.org/10.1111/j.1462-2920.2012.02710.x