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Applied and Environmental Microbiology, October 1999, p. 4618-4629, Vol. 65, No. 10
Max Planck Institute for Marine Microbiology,
D-28359 Bremen, Germany1; Department of
Microbial Ecology, Institute of Biology, DK-8000 Aarhus C,
Denmark2; and Paques Bio Systems BV,
Received 26 March 1999/Accepted 16 June 1999
Using molecular techniques and microsensors for H2S and
CH4, we studied the population structure of and the
activity distribution in anaerobic aggregates. The aggregates
originated from three different types of reactors: a methanogenic
reactor, a methanogenic-sulfidogenic reactor, and a sulfidogenic
reactor. Microsensor measurements in methanogenic-sulfidogenic
aggregates revealed that the activity of sulfate-reducing bacteria (2 to 3 mmol of S2
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Distribution of Sulfate-Reducing and Methanogenic
Bacteria in Anaerobic Aggregates Determined by Microsensor and
Molecular Analyses
m
3 s
1 or
2 × 10
9 mmol s
1 per aggregate) was
located in a surface layer of 50 to 100 µm thick. The sulfidogenic
aggregates contained a wider sulfate-reducing zone (the first 200 to
300 µm from the aggregate surface) with a higher activity (1 to
6 mmol of S2
m
3 s
1 or 7 × 10
9 mol s
1 per aggregate). The
methanogenic aggregates did not show significant sulfate-reducing
activity. Methanogenic activity in the methanogenic-sulfidogenic aggregates (1 to 2 mmol of CH4 m
3
s
1 or 10
9 mmol s
1 per
aggregate) and the methanogenic aggregates (2 to 4 mmol of CH4 m
3 s
1 or 5 × 10
9 mmol s
1 per aggregate) was located more
inward, starting at ca. 100 µm from the aggregate surface. The
methanogenic activity was not affected by 10 mM sulfate during a 1-day
incubation. The sulfidogenic and methanogenic activities were
independent of the type of electron donor (acetate, propionate,
ethanol, or H2), but the substrates were metabolized in
different zones. The localization of the populations corresponded to
the microsensor data. A distinct layered structure was found in the
methanogenic-sulfidogenic aggregates, with sulfate-reducing bacteria in
the outer 50 to 100 µm, methanogens in the inner part, and
Eubacteria spp. (partly syntrophic bacteria) filling the
gap between sulfate-reducing and methanogenic bacteria. In methanogenic aggregates, few sulfate-reducing bacteria were detected, while methanogens were found in the core. In the sulfidogenic aggregates, sulfate-reducing bacteria were present in the outer 300 µm, and methanogens were distributed over the inner part in clusters with syntrophic bacteria.
*
Corresponding author. Mailing address: Max Planck
Institute for Marine Microbiology, Celsiusstrasse 1, D-28359 Bremen,
Germany. Phone: 49-421-2028836. Fax: 49-421-2028580. E-mail:
dbeer{at}mpi-bremen.de.
Applied and Environmental Microbiology, October 1999, p. 4618-4629, Vol. 65, No. 10
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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