Archaeal versus bacterial ammonia oxidation in aquatic and semiterrestrial environments - in situ relevance and regulating factors

• Applicant: Dr. Martina Herrmann
• Subject Area: Microbial Ecology and Applied Microbiology
• Term: from 2009 to 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 111901763

Our understanding of nitrification has changed substantially in just the last few years. The ubiquity and high abundance of ammonia oxidizing archaea (AOA) suggest that they may be more important for nitrification than ammonia oxidizing bacteria (AOB). In particular, recent investigations indicate a special role of AOA in low pH environments and in freshwater macrophyte rhizospheres. However, only little is known about how much AOA really contribute to in situ ammonia oxidation. The proposed project aims to assess the ecological relevance of archaeal versus bacterial ammonia oxidation, using freshwater sediments and peatland soils as model systems. Two key hypotheses will be addressed: (1) Predominance of bacterial ammonia oxidation shifts towards predominance of archaeal ammonia oxidation along a gradient of decreasing pH and decreasing ammonia availability. (2) Mixotrophic utilization of organic root exudates supports high abundances of AOA in plant rhizospheres. AOA and AOB diversity, abundance, and functional gene expression will be linked to nitrification activity in both field investigations and microcosm experiments. Uptake of root exudates by putative AOA will be assessed using stable isotope assays in combination with Raman-FISH.

• DFG Programme: Research Grants