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Appl Environ Microbiol, March 1998, p. 960-969, Vol. 64, No. 3
Max-Planck-Institut für terrestrische
Mikrobiologie, D-35043 Marburg, Germany
Received 19 August 1997/Accepted 17 December 1997
A dual approach consisting of cultivation and molecular retrieval
of partial archaeal 16S rRNA genes was carried out to characterize the
diversity and structure of the methanogenic community inhabiting the
anoxic bulk soil of flooded rice microcosms. The molecular approach
identified four groups of known methanogens. Three environmental sequences clustered with Methanobacterium bryantii and
Methanobacterium formicicum, six were closely related but
not identical to those of strains of Methanosaeta concilii,
two grouped with members of the genus Methanosarcina, and
two were related to the methanogenic endosymbiont of Plagiopyla
nasuta. The cultivation approach via most-probable-number counts
with a subsample of the same soil as an inoculum yielded cell numbers
of up to 107 per g of dry soil for the
H2-CO2-utilizing methanogens and of up to
106 for the acetate-utilizing methanogens. Strain VeH52,
isolated from the terminal positive dilution on
H2-CO2, grouped within the phylogenetic
radiation characterized by M. bryantii and M. formicicum and the environmental sequences of the
Methanobacterium-like group. A consortium of two distinct
methanogens grew in the terminal positive culture on acetate. These two
organisms showed absolute 16S rRNA gene identities with environmental
sequences of the novel Methanosaeta-like group and the
Methanobacterium-like group. Methanosarcina spp. were identified only in the less-dilute levels of the same dilution series on acetate. These data correlate well with acetate concentrations of about 11 µM in the pore water of this rice paddy soil. These concentrations are too low for the growth of known Methanosarcina spp. but are at the acetate utilization
threshold of Methanosaeta spp. Thus, our data indicated
Methanosaeta spp. and Methanobacterium spp. to
be the dominant methanogenic groups in the anoxic rice soil, whereas
Methanosarcina spp. appeared to be less abundant.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Diversity and Structure of the Methanogenic
Community in Anoxic Rice Paddy Soil Microcosms as Examined by
Cultivation and Direct 16S rRNA Gene Sequence Retrieval
and
*
Corresponding author. Mailing address:
Max-Planck-Institut für terrestrische Mikrobiologie,
Karl-von-Frisch-Straße, D-35043 Marburg, Germany. Phone: 49 (6421) 178 720. Fax: 49 (6421) 178 809. E-mail:
liesack{at}mailer.uni-marburg.de.
Present address: Department of Microbiology and Immunology,
University of Melbourne, Parkville, Victoria 3052, Australia.
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