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Nitrogen fixation at 92 degrees C by a hydrothermal vent archaeon
Mausmi P Mehta1, John A Baross
1School of Oceanography, University of Washington, Seattle, WA 98195, USA. mausmi@alum.mit.edu
Science (New York, N.Y.)
|December 16, 2006
Summary
Scientists discovered a hyperthermophilic archaeon capable of biological nitrogen fixation at 92°C, expanding the known temperature limits for this vital process in extreme environments.
Area of Science:
- Microbiology
- Biochemistry
- Extremophile Research
Background:
- Biological nitrogen fixation is crucial for life, converting atmospheric nitrogen (N2) into ammonia (NH3).
- The known upper temperature limit for biological nitrogen fixation was previously 64°C.
- Deep-sea hydrothermal vents harbor unique microbial communities adapted to extreme temperatures and pressures.
Purpose of the Study:
- To investigate the potential for biological nitrogen fixation in hyperthermophilic microorganisms.
- To identify and characterize novel nitrogen-fixing organisms from deep-sea hydrothermal vents.
- To determine the upper temperature boundary for nitrogen fixation.
Main Methods:
- Isolation and cultivation of microorganisms from deep-sea hydrothermal vent fluid.
- 16S ribosomal RNA gene sequencing for phylogenetic analysis.
- Measurement of nitrogen fixation activity using isotope labeling ((15)N2).
- Analysis of nitrogenase gene (nifH) expression via messenger RNA detection.
Main Results:
- A novel methanogenic archaeon, FS406-22, was isolated from deep-sea hydrothermal vent fluid.
- FS406-22 demonstrated nitrogen fixation (N2 to NH3 reduction) at temperatures up to 92°C.
- This temperature is 28°C higher than the previously established upper limit for biological nitrogen fixation.
- Phylogenetic analysis showed FS406-22 is closely related (99% 16S rRNA similarity) to Methanocaldococcus jannaschii.
- FS406-22 incorporated (15)N2 and expressed nifH mRNA at its optimal growth temperature of 90°C.
Conclusions:
- The discovery of FS406-22 significantly extends the known temperature range for biological nitrogen fixation.
- This finding suggests a broader potential for life and nitrogen cycling in the subseafloor biosphere.
- It implies that nitrogen-limited ecosystems, even under extreme heat, may support biological nitrogen fixation.
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