Nitrogen Fixation at 92°C by a Hydrothermal Vent Archaeon

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Abstract
A methanogenic archaeon isolated from deep-sea hydrothermal vent fluid was found to reduce N 2 to NH 3 at up to 92°C, which is 28°C higher than the current upper temperature limit of biological nitrogen fixation. The 16 S ribosomal RNA gene of the hyperthermophilic nitrogen fixer, designated FS406-22, was 99% similar to that of non–nitrogen fixing Methanocaldococcus jannaschii DSM 2661. At its optimal growth temperature of 90°C, FS406-22 incorporated 15 N 2 and expressed nifH messenger RNA. This increase in the temperature limit of nitrogen fixation could reveal a broader range of conditions for life in the subseafloor biosphere and other nitrogen-limited ecosystems than previously estimated.