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Nitrification at Low pH by Aggregated Chemolithotrophic Bacteria
W De Boer1, P J Gunnewiek, M Veenhuis
1Institute for Ecological Research, P.O. Box 40, 6666 ZG Heteren, and Laboratory for Electron Microscopy, Biological Centre, University of Groningen, 9751 NN Haren, The Netherlands, and Abteilung für Mikrobiologie, Institut für Allgemeine Botanik der Universität Hamburg, D-2000 Hamburg 52, Germany.
Applied and Environmental Microbiology
|December 1, 1991
Summary
Acid-tolerant microorganisms in soil perform nitrification at low pH. Aggregated ammonium-oxidizing bacteria protect cells from nitrous acid toxicity, enabling nitrate formation in acidic environments.
Area of Science:
- Microbiology
- Environmental Science
- Soil Science
Background:
- Nitrification is crucial for soil fertility but often inhibited in acidic soils.
- Understanding acid-tolerant nitrification mechanisms is vital for soil health in acidic environments.
Purpose of the Study:
- To investigate the mechanism of acid-tolerant, chemolithotrophic nitrification.
- To identify microorganisms capable of nitrification at pH 4.
Main Methods:
- Enrichment of nitrifying microorganisms from Dutch acid soils at pH 4.
- Acetylene inhibition assays and carbon dioxide limitation experiments to confirm chemolithoautotrophic nature.
- Electron microscopy to observe microbial morphology and aggregation.
- Filtration experiments to assess nitrification by aggregated versus single cells.
Main Results:
- Enriched cultures exhibited chemolithoautotrophic nitrate production, inhibited by acetylene and limited by carbon dioxide.
- Electron microscopy revealed aggregated bacteria, including ammonium oxidizers, morphologically similar to known nitrifying genera.
- Aggregated cells nitrified at low pH, while single cells did not, suggesting protection against nitrous acid.
Conclusions:
- Aggregated chemolithoautotrophic bacteria are likely responsible for nitrification in many acid soils.
- Cell aggregation may protect nitrifying bacteria from nitrous acid toxicity in acidic conditions.
- This process bypasses the need for high pH microsites or organic carbon, broadening the understanding of nitrogen cycling in acidic soils.