AMMONIA-OXIDIZING ARCHAEA AND BACTERIA IN THE RHIZOSPHERE OF FRESHWATER MACROPHYTES Martina Herrmann and Andreas Schramm Department of Biological Sciences, Microbiology, University of Aarhus, Denmark Aquatic macrophytes such as Littorella uniflora and Lobelia dortmanna release oxygen from their roots and thereby stimulate nitrification and coupled nitrification-denitrification in their rhizosphere. However, oxygen release and inorganic nitrogen concentrations differ markedly between macrophyte species. We therefore propose (i) that the rhizosphere of freshwater macrophytes harbours a species-specific microbial community distinct from that of unvegetated sediment and (ii) that aquatic macrophytes have an impact on abundance and activity of nitrifying and denitrifying bacteria in freshwater sediment. The goal of this study was to test these hypotheses for the key functional group for coupled nitrification-denitrification, the ammonia-oxidizing prokaryotes. Six different sites and three macrophyte species with contrasting root systems and rhizosphere microenvironments, i.e. Littorella uniflora, Juncus bulbosus, and Myriophyllum alterniflorum, were selected for comparative investigations. Porewater analyses and potential rate measurements revealed clear differences in ammonia oxidation rates. The diversity of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) was assessed using the ammonia monooxygenase (amoA) gene as functional marker. Both AOA and AOB could be detected in the rhizosphere of all three plant species, whereas AOA were absent in some unvegetated sediments. Distribution patterns of AOA and AOB phylotypes suggest that plant species as well as site-dependant sediment properties influence nitrifier community composition. Preliminary quantitative results from fluorescence in situ hybridization and PCR indicate higher abundances of nitrifying prokaryotes in the rhizosphere compared to unvegetated sediment, and a dominance of AOA over AOB in most rhizospheres. Whether AOA also dominate ammonia oxidation activity remains to be investigated.
Biospektrum. Proceedings of the Vaam Annual Meeting, 2007
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Annual Conference of the Association for General and Applied Microbiology (VAAM), 2007