Biodiversity and ecophysiology of nitrifying bacterial communities
Fig.1: The redox cycle of nitrogen.
Fig. 2: 16S rRNA-based tree showing the phylogenetic affiliation of AOB (green) and NOB (red). The scale bar indicates 0.1 estimated change per nucleotide.
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Nitrification comprises the oxidation of ammonia to nitrite and the subsequent oxidation of nitrite to nitrate and is a key process of the biogeochemical nitrogen cycle (Fig. 1). The two oxidation steps are catalyzed by two guilds of aerobic, chemolithoautotrophic bacteria: ammonia-oxidizing (AOB) and nitrite-oxidizing bacteria (NOB) (Fig. 2). Collective terms for AOB and NOB are "nitrifiers" and "nitrifying bacteria".
Nitrifiers are ubiquitous in soil, freshwater, and marine environments and have been found in unusual habitats such as building sandstone (Bock and Koops, 1992; Koops et al., 2003). They play key roles for nitrogen turnover in these ecosystems and are important for nitrogen removal from wastewater. Ammonia and nitrite are toxic to aquatic life and the release of these pollutants from sewage into receiving waters must be minimized. Excess nitrogen input from wastewater contributes to the eutrophication of natural waters, which causes incalculable ecological damage. Unfortunately, wastewater treatment plants often suffer from unpredictable breakdowns of nitrification performance, and nitrifying activity contributes to nitrogen losses from agricultural soils. Detailed insight into the biodiversity and ecophysiology of nitrifiers is urgently needed for optimizing performance and stability of wastewater treatment plants and for improving the efficiency of soil fertilization.
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Molecular approaches like comparative 16S rRNA sequence analyses and fluorescence in situ hybridization (FISH) with rRNA-targeted probes have revealed that yet uncultured nitrifying bacteria are abundant in natural and engineered habitats. Many of these obviously important nitrifiers have resisted all cultivation attempts so far. This project studies the diversity, distribution, and ecophysiology of uncultured nitrifiers, and their interactions with other microorganisms in natural habitats and wastewater treatment plants. For this purpose, we apply a wide range of cultivation-independent methods, including phylogenetic analyses of marker gene sequences, FISH and FISH-microautoradiography (Lee et al., 1999),  confocal laser scanning microscopy combined with digital image analysis, DNA microarray techniques, and environmental genomics.
Please follow these links for more information about our work on ammonia-oxidizing bacteria and nitrite-oxidizing bacteria.
Investigated by:
Holger Daims, Kilian Stoecker, Frank Maixner, Sebastian Lücker,
Roland Hatzenpichler, Jan Dolinsek, Diana Lebherz,
Christiane Dorninger, Nathalie Schuster, Hanna Koch
Selected literature:
- Bock, E. and Koops, H.-P. (1992). The genus Nitrobacter and related genera. In: The prokaryotes. Balows, A., Trüper, H. G., Dworkin, M., Harder, W. and Schleifer, K.-H. (Eds.), 2302-2309, Springer-Verlag, New York.
- Koops, H. P., Purkhold, U., Pommerening-Röser, A., Timmermann, G. and Wagner, M. (2003). The lithoautotrophic ammonia oxidizers. In: The Prokaryotes: An evolving electronic resource for the microbiological community. M. Dworkin et al. (Eds.), Springer Verlag, New York.
- Lee, N., Nielsen, P. H., Andreasen, K. H., Juretschko, S., Nielsen, J. L., Schleifer, K.-H. and Wagner, M. (1999). Combination of fluorescent in situ hybridization and microautoradiography - a new tool for structure-function analyses in microbial ecology. Appl. Environ. Microbiol. 65: 1289-1297.
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