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Applied and Environmental Microbiology, May 1999, p. 1826-1833, Vol. 65, No. 5
Department of Biogeochemistry, Max-Planck
Institute for Terrestrial Microbiology, Marburg, Germany
Received 11 December 1998/Accepted 23 February 1999
Methanotrophic and nitrifying bacteria are both able to oxidize
CH4 as well as NH4+. To date it is
not possible to estimate the relative contribution of methanotrophs to
nitrification and that of nitrifiers to CH4 oxidation and
thus to assess their roles in N and C cycling in soils and sediments.
This study presents new options for discrimination between the
activities of methanotrophs and nitrifiers, based on the competitive
inhibitor CH3F and on recovery after inhibition with
C2H2. By using rice plant soil as a model
system, it was possible to selectively inactivate methanotrophs in soil
slurries at a
CH4/CH3F/NH4+ molar
ratio of 0.1:1:18. This ratio of CH3F to
NH4+ did not affect ammonia oxidation, but
methane oxidation was inhibited completely. By using the same model
system, it could be shown that after 24 h of exposure to
C2H2 (1,000 parts per million volume), methanotrophs recovered within 24 h while nitrifiers stayed
inactive for at least 3 days. This gave an "assay window" of
48 h when only methanotrophs were active. Applying both assays to
model microcosms planted with rice plants demonstrated a major
contribution of methanotrophs to nitrification in the rhizosphere,
while the contribution of nitrifiers to CH4 oxidation was insignificant.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Contribution of Methanotrophic and Nitrifying
Bacteria to CH4 and NH4+ Oxidation
in the Rhizosphere of Rice Plants as Determined by New Methods of
Discrimination
*
Corresponding author. Mailing address:
Max-Planck-Institut für terrestrische Mikrobiologie,
Karl-von-Frischstrasse, D-35043, Marburg, Germany. Phone: 49 6421 178821. Fax: 49 6421 178809. E-mail:
bodelier{at}mailer.uni-marburg.de.
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