The proposed project centres on so far neglected animal-microbe interactions in freshwater sediment that are expected to greatly influence denitrification rates and N2O emission to the atmosphere. We hypothesise that the guts of sediment-dwelling detritivores constitute "mobile microsites" in which bacterial denitrification will be induced by anoxia and high concentrations ofdissolved organic carbon. Over time, the inoculation of sediment with actively denitrifying bacteria via egested feces may favour the development of a structurally and functionally distinct denitrifying community.
In a fully integrated approach using the contemporary techniques of Microbial Ecology we aim at:
(i) characterising the gut microenvironment of the abundant detritivore Chironomus r iparius (Insecta: Diptera) withmicrosensors and HPLC analysis,
(ii) quantifying NO3- consumption and N2O production in gut and sediment using the 15N isotope pairing technique and gaschromatography, and
(iii) determining community structure and gene expression of denitrifying bacteria in gut and sediment using the genes coding for NO3- reductase (narG) and N2O reductase (nosZ) as well as their mRNA transcripts.
We will test the "mobile microsite" hypothesis in laboratory experiments, using freshwater sediment stocked with C. ripariuslarvae. The general applicability of the hypothesis will be evaluated at several NO3- polluted field sites in Denmark using sediment enclosures experimentally enriched in C. riparius larvae. These investigations will be complemented b y screening other benthic detritivores present at the field sites for denitrification and N2O emission. We expect that the results of this study will improve predictive models of eutrophication (e.g., NO3- dynamics) and global climate change (e.g., N2O emission).
Field of science
- /natural sciences/biological sciences/microbiology/bacteriology
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