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Applied and Environmental Microbiology, February 2006, p. 1013-1018, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.1013-1018.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

In Vivo Emission of Dinitrogen by Earthworms via Denitrifying Bacteria in the Gut

Marcus A. Horn,1 Ralph Mertel,1 Matthias Gehre,2 Matthias Kästner,2 and Harold L. Drake1*

Department of Ecological Microbiology, University of Bayreuth, 95445 Bayreuth,1 Department of Bioremediation, Center for Environmental Research Leipzig-Halle, 04318 Leipzig, Germany2

Received 15 September 2005/ Accepted 8 November 2005

Earthworms emit the greenhouse gas nitrous oxide (N2O), and ingested denitrifiers in the gut appear to be the main source of this N2O. The primary goal of this study was to determine if earthworms also emit dinitrogen (N2), the end product of complete denitrification. When [15N]nitrate was injected into the gut, the earthworms Aporrectodea caliginosa and Lumbricus terrestris emitted labeled N2 (and also labeled N2O) under in vivo conditions; emission of N2 by these two earthworms was relatively linear and approximated 1.2 and 6.6 nmol N2 per h per g (fresh weight), respectively. Isolated gut contents also produced [15N]nitrate-derived N2 and N2O under anoxic conditions. N2 is formed by N2O reductase, and acetylene, an inhibitor of this enzyme, inhibited the emission of [15N]nitrate-derived N2 by living earthworms. Standard gas chromatographic analysis demonstrated that the amount of N2O emitted was relatively linear during initial incubation periods and increased in response to acetylene. The calculated rates for the native emissions of N2 (i.e., without added nitrate) by A. caliginosa and L. terrestris were 1.1 and 1.5 nmol N2 per h per g (fresh weight), respectively; these emission rates approximated that of N2O. These collective observations indicate that (i) earthworms emit N2 concomitant with the emission of N2O via the in situ activity of denitrifying bacteria in the gut and (ii) N2O is quantitatively an important denitrification-derived end product under in situ conditions.

* Corresponding author. Mailing address: Department of Ecological Microbiology, University of Bayreuth, 95445 Bayreuth, Germany. Phone: (49) (0)921-55561. Fax: (49) (0)921-555793. E-mail: hld{at}uni-bayreuth.de.

Applied and Environmental Microbiology, February 2006, p. 1013-1018, Vol. 72, No. 2
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.2.1013-1018.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Wust, P. K., Horn, M. A., Henderson, G., Janssen, P. H., Rehm, B. H. A., Drake, H. L. (2009). Gut-Associated Denitrification and In Vivo Emission of Nitrous Oxide by the Earthworm Families Megascolecidae and Lumbricidae in New Zealand. Appl. Environ. Microbiol. 75: 3430-3436 [Abstract] [Full Text]  
  • Wust, P. K., Horn, M. A., Drake, H. L. (2009). In Situ Hydrogen and Nitrous Oxide as Indicators of Concomitant Fermentation and Denitrification in the Alimentary Canal of the Earthworm Lumbricus terrestris. Appl. Environ. Microbiol. 75: 1852-1859 [Abstract] [Full Text]  
  • Stief, P., Poulsen, M., Nielsen, L. P., Brix, H., Schramm, A. (2009). Nitrous oxide emission by aquatic macrofauna. Proc. Natl. Acad. Sci. USA 106: 4296-4300 [Abstract] [Full Text]  
  • Horn, M. A., Drake, H. L., Schramm, A. (2006). Nitrous Oxide Reductase Genes (nosZ) of Denitrifying Microbial Populations in Soil and the Earthworm Gut Are Phylogenetically Similar. Appl. Environ. Microbiol. 72: 1019-1026 [Abstract] [Full Text]  


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