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Nitrogen fixation by symbiotic and free-living spirochetes
T G Lilburn1, K S Kim, N E Ostrom
1Ribosomal Database Project, Center for Microbial Ecology, Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824-1101, USA.
Science (New York, N.Y.)
|June 30, 2001
Summary
Spirochetes, previously unknown to fix nitrogen, possess nitrogenase activity. This discovery implicates them in termite nutrition and global nitrogen cycling, potentially explaining unassigned nitrogenase genes.
Area of Science:
- Microbiology
- Biochemistry
- Environmental Science
Background:
- Spirochetes are a diverse group of bacteria, commonly found in various environments including animal guts and sediments.
- Nitrogen fixation, the conversion of atmospheric nitrogen into ammonia, is a crucial process for life.
- The nitrogenase gene (nifH) is a key indicator of nitrogen fixation capability.
Purpose of the Study:
- To investigate the presence of nitrogenase gene homologs and nitrogenase activity in spirochetes.
- To determine the role of spirochetes in nitrogen nutrition, particularly in termites.
- To explore the implications of spirochete nitrogen fixation in global nitrogen cycling.
Main Methods:
- Screening spirochete genomes from termite hindguts and freshwater sediments for nifH gene homologs.
- Assaying nitrogenase activity in selected spirochete isolates, including termite gut Treponema ZAS-9 and Spirochaeta aurantia.
- Analyzing the presence of nifH homologs in oral and ruminal treponemes.
Main Results:
- Spirochetes from termite guts and sediments were found to possess nifH gene homologs.
- Demonstrated nitrogenase activity in these spirochetes, a novel finding for this phylum.
- Identified nifH homologs in human oral and bovine ruminal treponemes.
- Confirmed 15-dinitrogen fixation in Treponema ZAS-9 and Spirochaeta aurantia.
Conclusions:
- Spirochetes possess the metabolic capability for nitrogen fixation.
- Spirochetes likely contribute to the nitrogen nutrition of termites and global nitrogen cycling.
- Spirochetes may represent a source of previously unassigned nifH genes in environmental samples.
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