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Applied and Environmental Microbiology, October 1998, p. 3674-3682, Vol. 64, No. 10
School of Biological Sciences,
Received 13 April 1998/Accepted 23 July 1998
The autotrophic ammonia-oxidizing bacteria in a eutrophic
freshwater lake were studied over a 12-month period. Numbers of ammonia
oxidisers in the lakewater were small throughout the year, and
tangential-flow concentration was required to obtain meaningful estimates of most probable numbers. Sediments from littoral and profundal sites supported comparatively large populations of these bacteria, and the nitrification potential was high, particularly in
summer samples from the littoral sediment surface. In enrichment cultures, lakewater samples nitrified at low (0.67 mM) ammonium concentrations only whereas sediment samples exhibited
nitrification at high (12.5 mM) ammonium concentrations also.
Enrichments at low ammonium concentration did not nitrify when
inoculated into high-ammonium medium, but the converse was not true.
This suggests that the water column contains a population of ammonia
oxidizers that is sensitive to high ammonium concentrations. The
observation of nitrification at high ammonium concentration by isolates
from some winter lakewater samples, identified as
nitrosospiras by 16S rRNA probing, is consistent with the
hypothesis that sediment ammonia oxidizers enter the water column at
overturn. With only one exception, nested PCR amplification enabled the
detection of Nitrosospira 16S rDNA in all samples, but
Nitrosomonas (N. europaea-eutropha lineage) 16S
rDNA was never obtained. However, the latter were part of the sediment
and water column communities, because their 16S rRNA could be detected
by specific oligonucleotide probing of enrichment cultures.
Furthermore, a specific PCR amplification regime for the
Nitrosomonas europaea ammonia monooxygenase gene (amoA) yielded positive results when applied directly to
sediment and lakewater samples. Patterns of
Nitrosospira and Nitrosomonas detection by
16S rRNA oligonucleotide probing of sediment enrichment cultures were
complex, but lakewater enrichments at low ammonium concentration were
positive for nitrosomonads and not nitrosospiras. Analysis
of enrichment cultures has therefore provided evidence for the
existence of subpopulations within the lake ammonia-oxidizing community
distinguishable on the basis of ammonium tolerance and possibly showing
a seasonal distribution between the sediment and water column.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Application of Molecular Biological Techniques to a Seasonal
Study of Ammonia Oxidation in a Eutrophic Freshwater
Lake
*
Corresponding author. Mailing address: School of
Biological Sciences, Life Sciences Building, University of Liverpool,
Liverpool L69 7ZB, United Kingdom. Phone: 151 794 4413. Fax: 151 794 4401. E-mail: aj55m{at}liverpool.ac.uk.
Applied and Environmental Microbiology, October 1998, p. 3674-3682, Vol. 64, No. 10
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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