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Applied and Environmental Microbiology, June 1999, p. 2402-2408, Vol. 65, No. 6
Limnological Research Center, Swiss Federal Institute for
Environmental Science and Technology (EAWAG), CH-6047 Kastanienbaum,
Switzerland1; Max-Planck-Institut
für Terrestrische Mikrobiologie, D-35043 Marburg/Lahn,
Germany2; Department of Chemical
Engineering, Chemistry and Environmental Sciences, New Jersey
Institute of Technology, Newark, New Jersey
071023; and Department of Biological
Sciences, Rutgers University, Newark, New Jersey
07102-18114
Received 14 December 1998/Accepted 31 March 1999
Anoxic sediments from Rotsee (Switzerland) were analyzed for the
presence and diversity of methanogens by using molecular tools and for
methanogenic activity by using radiotracer techniques, in addition to
the measurement of chemical profiles. After PCR-assisted sequence
retrieval of the 16S rRNA genes (16S rDNA) from the anoxic sediment of
Rotsee, cloning, and sequencing, a phylogenetic analysis identified two
clusters of sequences and four separated clones. The sequences in
cluster 1 grouped with those of Methanosaeta spp., whereas
the sequences in cluster 2 comprised the methanogenic endosymbiont of
Plagiopyla nasuta. Discriminative oligonucleotide probes
were constructed against both clusters and two of the separated clones.
These probes were used subsequently for the analysis of indigenous
methanogens in a core of the sediment, in addition to domain-specific
probes against members of the domains Bacteria and
Archaea and the fluorescent stain
4',6-diamidino-2-phenylindole (DAPI), by fluorescent in situ
hybridization. After DAPI staining, the highest microbial density was
obtained in the upper sediment layer; this density decreased with depth
from (1.01 ± 0.25) × 1010 to (2.62 ± 0.58) × 1010 cells per g of sediment (dry weight). This zone
corresponded to that of highest metabolic activity, as indicated by the
ammonia, alkalinity, and pH profiles, whereas the methane profile was
constant. Probes Eub338 and Arch915 detected on average 16 and 6% of
the DAPI-stained cells as members of the domains Bacteria
and Archaea, respectively. Probe Rotcl1 identified on
average 4% of the DAPI-stained cells as Methanosaeta spp.,
which were present throughout the whole core. In contrast, probe Rotcl2
identified only 0.7% of the DAPI-stained cells as relatives of the
methanogenic endosymbiont of P. nasuta, which was present
exclusively in the upper 2 cm of the sediment. Probes Rotp13 and Rotp17
did not detect any cells. The spatial distribution of the two
methanogenic populations corresponded well to the methane production
rates determined by incubation with either [14C]acetate
or [14C]bicarbonate. Methanogenesis from acetate
accounted for almost all of the total methane production, which concurs
with the predominance of acetoclastic Methanosaeta spp.
that represented on average 91% of the archaeal population.
Significant hydrogenotrophic methanogenesis was found only in the
organically enriched upper 2 cm of the sediment, where the probably
hydrogenotrophic relatives of the methanogenic endosymbiont of P. nasuta, accounting on average for 7% of the archaeal population,
were also detected.
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Vertical Distribution of Methanogens in the Anoxic
Sediment of Rotsee (Switzerland)
*
Corresponding author. Mailing address: Swiss Federal
Institute for Environmental Science and Technology (EAWAG),
Limnological Research Center, Seestrasse 79, CH-6047 Kastanienbaum,
Switzerland. Phone: 41-41-349 2153. Fax: 41-41-349 2168. E-mail:
kornelia.zepp{at}eawag.ch.
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