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Applied and Environmental Microbiology, February 2001, p. 632-645, Vol. 67, No. 2
Limnological Institute, University of
Constance, D-78457 Konstanz,1 Lehrstuhl
für Mikrobiologie, Technische Universität München,
D-85350 Freising,2 Max-Planck Institute
for Marine Microbiology, D-28359 Bremen,3 and
Institute for Chemistry and Biology of the Marine Environment,
University of Oldenburg, D-26111 Oldenburg,4
Germany
Received 10 April 2000/Accepted 5 November 2000
We analyzed the composition of aggregate (lake snow)-associated
bacterial communities in Lake Constance from 1994 until 1996 between a
depth of 25 m and the sediment surface at 110 m by fluorescent in
situ hybridization with rRNA-targeted oligonucleotide probes of various
specificity. In addition, we experimentally examined the turnover of
dissolved amino acids and carbohydrates together with the microbial
colonization of aggregates formed in rolling tanks in the lab.
Generally, between 40 and more than 80% of the microbes enumerated by
DAPI staining (4',6'-diamidino-2-phenylindole) were detected as
Bacteria by the probe EUB338. At a depth of 25 m, 10.5% ± 7.9% and 14.2% ± 10.2% of the DAPI cell counts were detected by
probes specific for
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.2.632-645.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
- and
-Proteobacteria Control the
Consumption and Release of Amino Acids on Lake Snow
Aggregates

- and
-Proteobacteria. These proportions increased to 12.0% ± 3.3% and 54.0% ± 5.9% at a depth of 50 m but decreased again at the sediment surface at 110 m to 2.7% ± 1.4% and 41.1% ± 8.4%, indicating a clear dominance of
-Proteobacteria at depths of 50 and 110 m, where
aggregates have an age of 3 to 5 and 8 to 11 days, respectively. From
50 m to the sediment surface, cells detected by a
Cytophaga/Flavobacteria-specific probe (CF319a) comprised
increasing proportions up to 18% of the DAPI cell counts.
-Proteobacteria always comprised minor proportions of
the aggregate-associated bacterial community. Using only two probes
highly specific for clusters of bacteria closely related to
Sphingomonas species and Brevundimonas
diminuta, we identified between 16 and 60% of the
-Proteobacteria. In addition, with three probes highly
specific for close relatives of the
-Proteobacteria Duganella
zoogloeoides (formerly Zoogloea ramigera),
Acidovorax facilis, and Hydrogenophaga
palleroni, bacteria common in activated sludge, 42 to 70% of the
-Proteobacteria were identified. In the early phase
(<20 h) of 11 of the 15 experimental incubations of aggregates,
dissolved amino acids were consumed by the aggregate-associated bacteria from the surrounding water. This stage was followed by a
period of 1 to 3 days during which dissolved amino acids were released
into the surrounding water, paralleled by an increasing dominance of
-Proteobacteria. Hence, our results show that lake snow
aggregates are inhabited by a community dominated by a limited number
of
- and
-Proteobacteria, which undergo a distinct
succession. They successively decompose the amino acids bound in the
aggregates and release substantial amounts into the surrounding water
during aging and sinking.
*
Corresponding author. Mailing address: Institute for
Chemistry and Biology of the Marine Environment, University of
Oldenburg, D-26111 Oldenburg, Germany. Phone: 49-441-798-5361. Fax:
49-441-798-3438. E-mail: m.simon{at}icbm.de.
Present address: Biotechnical Institute, DK-2970 Hørsholm, Denmark.
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